Purpose: The objective of the present study is to determine the impacts on their nutritional knowledge of the nutrition training provided to the adult male prisoners in the Closed Prison. Method and material: Experimental, which is a quantitative research method, has been used in the present study. Data were derived from pretest, posttest and monitoring test questionnaires completed by prisoners. The population for the study consisted of 504 adult male prisoners from the Amasya Type E Closed Prison Institution. 216 adult male prisoners were selected through voluntary selection. The 216 adult male prisoners were randomly divided into four groups, control (54), education (54), brochure (54) and education+brochure (54). Research data were collected with the help of a survey form using the face-to-face interview technique. Thirty-one multiple-choice questions were on the questionnaire. Statistical software was used to analyze change scores for pre-, posttest and monitoring test measures with the independent sample t test and single direction variance analysis (ANOVA) tests. Results: Analyzing the impact of education on nutritional knowledge, it has been found that the average score in the education group in the pretest measurement was 6.22 and the average score in the posttest measurement was 21.34. This difference between the scores was significant (p<0.05). In the "brochure+education" group, a significant difference was found between the posttest scores and monitoring test scores (p<0.05). Conclusion: The results of the study show that inmate participants could benefit from nutrition education and suggest that further investigations should be performed in a larger study population.