The purpose of the research was to explore the effects of e-portfolios on knowledge amassing. The participants were junior students who major in Multimedia Design and take the Digital Game course from one University in Taiwan. 43 students were selected randomly and assigned to the experimental group, while 45 were selected randomly and assigned to the control group. There were totally 88 students with 48 males and 40 females. The experimental group used blog to construct their e-portfolios, while the control did not construct e-portfolios. The teaching experiment lasted 9 weeks with 3 hour per week. The results revealed that the post-tests of overall knowledge amassing and its four constructs were all significantly greater than the pre-tests. Besides, the post-tests of overall knowledge amassing and its four constructs for the experimental group were all significantly greater than those of the control group. It implied that blog-based e-portfolios had significantly positive effect in knowledge amassing.