Purpose: The design of this study is a nonequivalent control group, non-synchronized quasi-experimental study. The purpose of this study is to examine the effects of laughter therapy on pain and anxiety of patients with postmastectomy. Methods: The participants were 33 patients admitted for mastectomy in a college affiliated hospital (17 patients in experimental group and 16 patients in control group from November, 2008 to March, 2009). The registered nurse who were certified as the 1st degree laughter specialist implemented the intervention once a day for 30 minutes from the 2nd day to the 6th day after surgery when visited them. Date were analyzed using t, Mann-Whitney U test, repeated measures of ANOVA, paired t-test, or ANCOVA. Results: The level of pain was significantly lower in the experimental group than in the control group. Since the level of pain in all participants was reduced as time passed, the interaction effect between time and group existed. The level of anxiety was significantly lower in the experimental group than in the control group. Conclusion: Based on the results, the laughter therapy may be recommended as an useful intervention to effectively reduce the levels of pain and anxiety among patients with postmastectomy.