The security in penitentiary system depends a lot on prison subculture. This subculture consists in adopting values, norms and principles that facilitate to fulfil one’s own needs in conditions of imprisonment. However, very often informal groups base their activities on patterns derived from the criminal subculture. The prison subculture often depreciates human dignity, being one of the most important factors disturbing the process of institutional rehabilitation. At the same time, there is a lack of scientific researches that can help to develop the field of behavioural studies in informal structures culture which have a significant influence on the state security due to the efficiency of penitentiary system and its rehabilitation function. To mitigate the gap in current investigations in this field, this research deals with prison subculture in Polish penitentiary system based on survey of penitentiary service officers. Our findings allow to conclude the significant changes in prison subculture during last decade. The most important are: increase of authority among inmates with a better material situation (23%), a greater degree of implementation of rehabilitation programmes by inmates (18.8%), as well as blurring the differences between prisoners mainly due to their joint participation in group activities (17%). To strengthen the further positive effect of penitentiary system on social norms and behaviour of prisoners it is advisable to eliminate potential sources and possibilities for obtaining, accumulating and transferring illegal income by convicted persons. This action defined as main tool to mitigate the subculture phenomenon and its impact of the rehabilitation process in penitentiary institutions.