This study investigated the influence of incarceration on the well-being of prison inmates in Nigeria. The study was carried out in Port Harcourt Prison in Rivers State, Nigeria. The population of inmates in this prison at the time of study was 2,997 while the sample of study was 250 inmates. The design of study was ex-post facto design. Five null hypotheses were formulated to guide the study and data for their investigation were collected through the administration of copies of a questionnaire tagged “influence of incarceration on prison inmates (ICPI) the reliability co-efficient of the five sub-sections of the instrument were 0.79; 0.80; 0.80; 0.80 and 0.80 while the overall reliability co-efficient was 0.80. The hypotheses were tested with t-test of independent means and the results show that nature of incarceration does not influence the physical and vocational well-being of prison inmates however, it influences their psychological, social and educational well-being. These results were discussed and some recommendations were also made. One of the recommendations is that psychological and counselling services designed for inmates who are depressed, filled with anxiety, fear and hopelessness should be improved and intensified.