The purpose of this study was to examine the effects of laughter therapy on mood, state anxiety, and serum cortisol based on a Stress-Coping Model for preoperative breast cancer patients. Methods: The study used a nonequivalent control group pretest-posttest design. The participants were 40 breast cancer patients who were admitted to one general hospital for surgery in 2009 (experimental group 23, control group 17). The experimental group received one hour laughter therapy consisting of dance, lots of laughter techniques, and meditation. Results: The mean ages were 47 years (experimental group) and 49 years (control group). There were no significant differences in demographic and disease-related characteristics between the two groups. After the intervention, the scores of mood and state-anxiety of experimental group were significantly improved than those of control group. However, no difference was found in serum cortisol. Conclusion: The laughter therapy was partially effective in improving stress response in patients with breast cancer. Further research is needed to develop and evaluate the longer periods of interventions to testify the effects on serum cortisol, and other biochemical variables.