Knowledge sharing in virtual learning communities requires intensive social interactions among community participants, such as articulating knowledge into written forms, posting messages to community’s discussion forum, responding comments to the messages posted by others; namely annotation. Annotation is an explicit expression of knowledge in the form of comments which reveal conceptual meanings of annotators’ implicit thought. This paper presents a personalized annotation management system (PAMS) and demonstrates how PAMS enhances knowledge sharing in virtual learning communities. Personalized annotation is used to equip the participants with Web-based authoring tools for commenting, knowledge articulation and exertion, which can be done by extracting explicit knowledge (in the form of metadata) from both the annotated objects and the annotation itself. An experiment has been conducted to evaluate how PAMS enhances knowledge sharing in students’ online group reading activity. The result of the experiment has demonstrated that PAMSenabled knowledge sharing do improve students’reading comprehension.