Purpose: This study aimed to examine the effects of education program by illness on perception of illness and knowledge of medication in psychiatric inpatients. Methods: The research design was a non-equivalent and non-synchronized control group design. For this research, a total of 50 subjects was selected at a psychiatric unit of C university hospital in U-city. The experimental group consisted of 24 subjects and they received education program by illness 1 session per a week for 4 weeks. The remaining 26 subjects were assigned to the control group and they received standard services except the education program by illness. In data analysis, SPSS/WIN 15.0 program was used. Results: The experimental group significantly improved compared to the control group in perception of illness and knowledge of medication. Conclusion: This study results suggest that education program by illness could be effective to improve perception of illness and knowledge of medication in psychiatric inpatients.