The objective of this study is to investigate the effects of multimedia annotations on improving reading comprehension of elementary school students with low reading ability. Three combinations of multimedia annotations (text + picture, narration + picture, and text + narration + picture) are adopted and compared to explore the most effective one. Thirty-three fourth graders with literacy problems were randomly and equally divided into three groups. Students in each group are required to complete online reading without and with annotation. After finishing the reading, all participants were asked to take the reading comprehension test immediately. The Wilcox signed-ranks test is adopted to analyze and compare the test outcomes. Questionnaires were also given to collect post-test feedback so that the effectiveness of the research can be further evaluated. The result of this study indicates narration + picture annotation may significantly improve reading comprehension of students with low reading ability. On the contrary, the combination of text, narration and picture annotation may have negative effect on reading comprehension. Overall, nearly 78.8% of the subjects agree that multimedia annotation may increase their motivation and improve their reading comprehension. In addition, 97% of the subjects consider multimedia annotation helpful in improving their understanding of articles.