The purpose of this study was to explore the self-evaluated effects of a web-based portfolio assessment system on various categories of students of motivation. The subjects for this study were the students of two computer classes in a Junior High School. The experimental group used the web-based portfolio assessment system whereas the control group used traditional assessment. The result reveals that the web-based portfolio assessment system was more effective or useful in the most of self-evaluated learning effects for low motivation students. (Contains 5 tables.)