Online comments have become an essential component of online media consumption. A meta-analysis was conducted to understand how online comment valence affects message perception, issue-relevant beliefs and attitudes, issue-relevant behaviors and behavioral intentions, communication behaviors and intentions, and emotions. Comment valence is defined as the distinction between positive comments, which align with, support, or favor the opinions expressed in the original message, and negative comments, which oppose, criticize, or disagree with the opinions expressed in the original message. After a comprehensive search and systematic screening and coding of existing studies, we identified 44 studies that are eligible to be included in the meta-analysis. We found that positive (vs. negative) comments led to significantly more positive evaluations of original messages (r = .22), stronger beliefs and attitudes that align with the positive comments (r = .29), higher likelihood to engage in behaviors that align with the positive comments (r = .09), higher likelihood to express opinions that align with the positive comments (r = .26), and more positive emotions (r = .16). Moreover, the number of comments, whether comment valence was mixed or not, and whether the original message was news or non-news moderated the effects of online comment valence on several outcomes. The findings suggest integrating these outcomes and moderators to develop a media effect theory and guide media practices in light of comment valence effects.