This paper reports on a study involving the design of online peer assessment (PA) activities to support university students’ small-group project-based learning in an introductory course. The study aimed to investigate the influences of different types of PA in terms of the rubric (quantitative ratings), peer feedback (qualitative comments) and hybrid (a combination of the rubric and peer feedback) on students’ project performance, and to explore further students’ perspectives on online PA. The quantitative findings suggested that (a) students in the hybrid condition likely had better project performance than those in the peer feedback condition did, and (b) students in the rubric condition could perform equally well as those in both of the hybrid and peer feedback conditions. The qualitative findings suggested that besides types of assessment, other possible confounding variables that might affect performance included perceived learning benefits, professional assessment, acceptance, and the online PA system.