The article covers Prussian knights’ opposition against the Teutonic Order at the beginning of 15th century – especially during the Great War with Poland and Lithuania. The main focal point of the work is set on the Battle of Grunwald. The geographical scope is that of Prussia and Culmerland and the chronological one is from the foundation of the Lizard League up to the knights’ court in Bratian (1414). Most of the knights mentioned belong to the politcaly active group, who wanted a bigger influence on the current matters of the state. This resulted in a number of activities before the Battle of Grunwald, including conspiracy (e.g. Jan Surwiłło [Hans Surwille]). Those activities did not cease after the battle. A very good example is Mikołaj z Pilewic [von Pfeilsdorf], who had been supplying the Teutonic Knights with false intelligence and had exchenged hostile to the Order letters with the Poles. For sure this kind of opposition was not very widespread. After the beginning of hostilities knights from Culmerland and Dobrzyn Land tried to acquire further privileges from the Order, e.g. the privilege from October 1409. It cannot be completely ruled out, that there was indeed an organized opposition before the Battle of Grunwald. It has been confirmed, that there were Polish-speaking knights in the Teutonic Order reconnaissance forces. In that light it is important to note Polish pennants found after the arrest of Mikołaj from Pilewice and curious results of the reconnaissance after Polish withdrawal from Kurzętnik. During the Battle of Grunwald the Culm Banner, which was a part of the last Teutonic Order strike, has surrendered to the Poles just after the death of the Grand Master. The knights have been taken captive, so we cannot speak of high treason, but nevertheless the surrender could have affected the battle’s outcome. After the Order was defeated some of the knights have openly backed the Polish side – they have pledged allegiance to Jagiełło and took part in storming of the Teutonic Order castles. In cooperation with rebellious knights the Poles have captured Ostróda, Kowalewo, Krzyżbork, Bałga and Kętrzyn. In effect, when Heinrich von Plauen became the Grand Master and Polish forces have withdrawn in September–October of 1410, those knights have been severely punished, without proper trials. The prosecution included, among others, Mikołaj from Plewice, Eberhard from Korsze, Jochart from Kętrzyn and a certain Zbylut (most likely identical with Zbylut Zebowski). Some knight fled to Poland (Mikołaj from Ryńsk [von Renis] or Stanisław from Bolumin [von Bolmen] and some obtained pardon of the Grand Master (e.g. Albrecht Karschau). Some of the fugitives later returned to Prussia, (Mikołaj from Ryńsk already in the autumn of 1410). Soon after, the knights contacted the ambitious komtur of Radzyń Jerzy Wirsberg. Probably they intended to overthrow Heinrich von Plauen and to force the new Grand Master to give more privileges to the knights. The conspiracy was revealed and both Jerzy Wirsberg and Mikołaj from Ryńsk were arrested. Mikołaj was later beheaded for treason. Other memebers of the conspiracy (Janusz from Pułkowo [von Pulkau], Fryderyk from Kitnowo [von Kintenau], Janusz from Szczuplinka [von Czipplin] and Gunter from Dylewo [von der Delau]) fled to Poland and tried to regain their properties. They, and also other fugitives (Jan Surwiłło, Kacper/Jacob from Kobyły [von Kobil]) were backed by both Jagiełło and Witold. Finally, after Heinrich von Plauen was overthrown most of the knights returned to Prussia and the knights’ tribunal acquitted the surviving members of Wirsberg conspiracy in 1414. There are some striking similarities between the knights opposing the Order rule. They are often members of the same family: brothers from Ryńsk and Kitowo, father and son from Dylewo, father-in-law and son-in-law (Mikołaj from Ryńsk and Gunter from Dylewo), first cousins (from Ryńsk, Kitnowo and Szczuplinki). Frequently they were also neighbours, especially among those who came from Culmerland (Pilewice, Płąchawy, Robakowo and Kobyły; Szczuplinki and Kitnowo; Słomowo and Bolumin; Ryńsk, Orzechowo and Pułkowo), but also from Korsze region (Eberhard Kunseck, Albrecht Karschau and probably Jochart) and Ostróda (Dylewo and Durąg). At least some of the knights owned money to the Order. There is no comprehensive data, but Dytryk and Gunter from Dylewo, Mikołaj from Ryńsk, Janusz from Pułkowo, Konrad from Płąchawy [von Planchau], Janusz from Szczuplinki, Konrad from Orzechowo [von Orsechaw], Mikołaj from Słomowo [von Slommau] and Janusz from Topolno [Toppolensky] were indebted. This could not be without influence on their attitude to the Order. To be fair one has to add, that there were also knights, who reminde faithful to the Order. The best known examples are Mikołaj Witkop from Targowo [von Tergewisch], Szymon Wagil and Albrechta from Wigwałd [von Wittchenwalde], who was given Sławkowo in 1411 „umb synes getruwen dinstes willen, den her unsern orden in den groesten noten hat beweist”. Some of the Lizard League members also remained faithful, e.g. Otton from Konojady [von Konoyad], who was not persecuted after the Battle of Grunwald (he appears in the sources in 1417). His family also worked with the Order: his brother Knrad (Kuncze) from Dąbrówka [von Damerau] was working in the Teutonic Order intelligence. At the beginning of the 15th century the Teutonic Order state was shaken by an internal struggle between the knights with the Order authorities. Both parties remained without a clear victory as their argument ended, for a time, in a stalemate. But the future would belong to the knights, and in an alliance with burgers, they eventually defeated the Teutonic Order.