The purpose of the study was to examine the effectiveness of assertiveness training in improving self-perceived levels of stress and assertiveness among nurses in Taiwan, Republic of China. The two-group experimental design was conducted in a 2,000-bed veteran general hospital. A sample of 60 volunteer Chinese-speaking nurses participated in the study. Subjects were randomly assigned to one of two treatments: assertiveness training (AT) or alternate treatment control (ATC), which served as a control and contained updated knowledge of new computer technology for in patient settings. Subjects in each group participated in six 2-hour workshops in the same two-week period. All subjects were pre-, post-, and follow-up posttested for stress and assertiveness with the Perceived Stress Scale (PSS) and Rathus Assertiveness Schedule (RAS), respectively. Results revealed the following: (1) subjects in both groups of pretest were clearly subassertive and under considerable stress; (2) by the end of training, the AT group scored significantly higher on the rating of assertiveness than those in the ATC group, and had successfully maintained their improvement by the 4-week follow-up; and (3) by the end of training, the AT group reported significantly lower levels of stress than the ATC group as indicated on the PSS, and successfully maintained their improvements at the 4-week follow-up. Overall, the results indicate clear support for the effectiveness of assertiveness training for treating subassertive behaviors and stress in a population of professional nurses in Taiwan.