This study's objective was to evaluate the effect of an assertiveness training program on nursing and medical students' assertiveness, self-esteem, and interpersonal communication satisfaction. Using a longitudinal research design, 69 participants whose scores on the Assertive Scale were < or = 50% (i.e., low assertiveness) and who were willing to participate were included and assigned to an experimental group (33 subjects) or comparison group (36 participants; participants were matched with the experimental group by grade and sex). Participants in the experimental group received eight 2-h sessions of assertiveness training once a week. Data were collected before and after training and again one month after the end of the training using the Rotter's Internal versus External Control of Reinforcement Scale, Sex Role Inventory, Assertive Scale, Esteem Scale, and Interpersonal Communication Satisfaction Inventory. The generalized estimated equation (GEE) method was used for statistical analysis. The assertiveness and self-esteem of the experimental group were significantly improved in nursing and medical students after assertiveness training, although interpersonal communication satisfaction of the experimental group was not significantly improved after the training program.