The purpose of this study was to identify the effects of sex education program on sex functioning and quality of life of the persons with chronic mental disorder. To achieve this purpose, nonequivalent control group pretest-posttest design was used to 59 clients(37 experimental group, 22 control group). The subjects were selected by a convenience sampling method. The data collection was carried out in day care program of the 2 mental health center in K city and rehabilitation ward of the K psychiatric hospital in N city from March to August(10 hours) in 2003. The SAS package program was used to analyse the data along with Frequency, Percentage, x²-test, Mann Whitney U test. The results of this study were as follows; 1. The experimental group received the sex education program showed a significantly higher sex functioning score than the control group(Z=-2.109, p=0.010). 2. The experimental group received the sex education program showed a significantly higher quality of life score than the control group(Z=-4.133, p=0.001). The study showed that the sex education program was effective in changed score of sex functioning and quality of life of the persons with chronic mental disorder. Based on the results of this study, we can recommend that sex education program should be done regularly in psychosocial rehabilitation program for persons with chronic mental disorder in mental health center.