Psychosocial climate is defined as the overall perception of social relations in a particular institution or group, and in the context of penal institutions it describes how prisoners and prison staff perceive a unit they live or work in. A positive psychosocial climate is important for the successful overall functioning of penal institutions - especially in terms of achieving highquality prisoners' treatment. The aim of this study was to examine the psychosocial climate in penal institutions in the Republic of Croatia. The study was conducted on a convenience sample of 674 adult prisoners in all penal institutions in the Republic of Croatia. The specific aims of this study were to validate the Prison Group Climate Inventory (PGCI) (Van der Helm, Stams and Van der Laan, 2011) and to assess the differences in perception of the living group climate regarding prisoners' previous imprisonment, terms of prison punishment - level of security, type of committed criminal offense and length of the prison sentence. Factor analysis confirmed four-factor solution of the PGCI instrument (support, growth, repression and atmosphere), and internal reliability coefficients proved to be satisfying for all PGCI dimensions. In Croatian sample of prisoners, all dimensions of psychosocial climate were estimated average or more toward negative values. Test of groups differences tests showed that prison stuff support, institutional atmosphere, openness of the psychosocial climate and the overall group climate in prisoners were more negatively estimated by prisoners with prior imprisonment experiences, those serving sentence in higher security facilities and offenders who committed both nonviolent and violent crimes.