Purpose: This study was done to assess effects of Assertive Community Treatment (ACT) in a community mental health center. Methods: This study was a non-equivalent control group design with two groups, each of 20 clients. The instruments were the Brief Psychiatric Rating Scale (BPRS), Global Assessment of Function (GAF), Satisfaction of Life, and the number and duration of admissions. Data collection was done in March, 2010 for the pre-test, and in March, 2011 for the post-test in the S community mental health center in Gyung-gi province. The collected data were analyzed using descriptive statistics, Fisher`s exact test, and Mann-Whitney U test with the SPSS/WIN program. Results: The experimental group showed significant differences in the duration of admission, GAF, and Satisfaction of Life,. but not on number of admissions and BPRS. Conclusion: The results of this study indicate that ACT can be applied as an effective case management model in Korea.