The study explores the characteristics of the relationship between the mental well-being and the belief in a just world among male juvenile offenders. 186 adolescents aged from 13 to 18 years (97 offenders and 89 law-abiding adolescents) were interviewed. Following methods were used for investigation of empirical constructs: “General Belief in a Just World Scale” (M. Schmitt, L. Montada, C. Dalbert), “General Belief in a Unjust World Scale” (J. Maes), “Belief in Immanent Justice Scale» (J. Maes)”, “General Belief in a Unjust World Scale Belief in Ultimate Justice Scale” (J. Maes), “5-Dimensional Belief in a Just Treatment Scale” (K. Stroebe), “Warwick–Edinburgh Mental Well-being scale” (R. Tennart). Revealed that mental well-being of law-abiding adolescents is positively associated with only two sources of justice: belief in God – for common destiny and belief in self as the source of justice for personal and common destiny. Offenders’ mental well-being is accompanied by an extensive complex of positive relations with beliefs in general, immanent, ultimate justice and also by belief in a diversity of sources of justice (God, nature, other people, self and chance). The study also shown that offenders’ mental well-being is positively associated with belief in an unjust world.