Purpose: The study was done to investigate effects of a horticultural therapy program on self-efficacy, stress response, and psychiatric symptoms in patients with schizophrenia. Methods: The research design was a quasi-experimental research with a nonequivalent control group non-synchronized pre-posttest. The participants were recruited from patients with schizophrenia admitted to 1 mental hospital located in D City. The research was carried out from August 3 to September 25, 2012. To test the effects of the horticultural therapy program, the participants were divided into two groups, an experimental group (29) and a control group (26). The horticulture therapy was provided to the experiment group for 60 minutes/session twice a week, for 8 weeks. Data were analyzed using Fisher`s exact probability test, x(2)-test, and t-test with the SPSS/WIN 12.0 program. Results: After attending the horticultural therapy program, the first hypothesis was verified as the score for self-efficacy in the experimental group was significantly higher than the control group (t=2.12, p=.039). The 3rd hypothesis was verified as the score for PANSS in the experimental group was significantly lower than the control group (t=-5.20, p<.001). Conclusion: These results indicate that the horticultural therapy program enhanced self-efficacy and lessened psychiatric symptoms in patients with schizophrenia.