University students must acquire good academic reading skills in undergraduate study. One of the effective skills is to insert annotations in the process of reading. With the advance of web technologies, students can jointly annotate an online article. However, the effectiveness of using online collaborative annotation platforms largely depends on the integration of instructional support. This paper elaborates on the design and effectiveness of using a peer assessment of online collaborative annotation approach in enhancing academic reading skills. Seventy-five first-year undergraduates were invited to annotate an article collaboratively in an online platform. They were requested to carry out peer assessment on the appropriateness of the annotations. Results from the data collected by a questionnaire suggest that the students considered the online platform enhanced collaborative learning, and the peer assessment component helped engage learning. They expressed their preferences to use the online annotation platform collaboratively in their future learning.