Conventionally, humor has been regarded as an indicator of mental health, but several researchers has proposed that the effects of humor in mental health may be different depending on humor styles. Therefore, further studies about humor style and the effect of humor are worthwhile. In the present study, we shall pay attention to buffering effect of humor on a decline in mental health. we attempted to identify weather the buffering effect of humor is different depending on humor styles in psychiatric patients. For this purpose correlation analysis on humor style, depression, anxiety and life satisfaction were carried out, and hierarchical regression analysis were applied to analyse moderating effect of humor style. Consequently, self-enhancing humor has a significant moderating effect on both depression and anxiety. Whereas, affiliative humor has a significant interactive effect with only depression. The conclusion which can be drawn from this study is that positive humor can work as a protective factor on a decline in mental health, and using self-enhancing humor is effective to increase life satisfaction. It might have a convergent meaning on adaptation that psychiatric patients could have a good adaptation(by using positive humor) in real world.