Transformation of the Prussian justice system and modernization in East Prussia in the second half of the 19th century led to the decision to build a new prison in Olsztyn. History of the Olsztyn prison during the Prussian period has not been so far the main subject of scientific research. This publication is an explication of the author's research related to the development of the prison system in former and current Polish lands. The prison in Olsztyn was the largest and most modern court prison in East Prussia. The purpose of this article is to attempt to determine selected aspects of the activity of the Olsztyn prison during the four decades of Prussian subordination. The preserved sources allow us to present the most important features of the Prussian penitentiary system. In addition, for the first time the prison staff was partially recreated, typical elements of everyday prison life were reconstructed and some events related to prison security were presented.