This study provided an assertiveness skills training program based on the process model of social skills and investigated the effect of assertiveness skills training on students at a women's university in Japan. It was a quasi-experimental study conducted in a pre- and post-survey design with nonequivalent groups. The training program included cognitive, emotional, and behavioral components. Students were divided into two groups: a group that received weekly 14 training sessions and a no training group. Effectiveness was measured in in terms of three functional effects: objectives effectiveness, relationship effectiveness, and self-respect effectiveness. Participants completed the assertion scale for adolescents and sense of authenticity scale pre- and post-training. Mann-Whitney U tests were conducted to compare the means of the pre and post differences between the two groups on persuasion negotiations (objectives effectiveness), relationship formation (relationship effectiveness), and sense of authenticity (self-respect effectiveness). Analysis results revealed increased behaviors in the training group related to objectives effectiveness through assertiveness compared to the no-training group, p = 0.05. There were no significant differences between the two groups in the amount of change in relationship effectiveness, p = 0.77, and self-respect effectiveness, p = 0.88. In the future, assertiveness skills training should include sessions that allow participants to integrate cognitive, emotional, and behavioral aspects, and effectiveness measurement should be more multidimensional.