We investigated the effects of aging and individual differences on credibility judgment of online health information. Analysis of credibility judgment ratings revealed that older adults were less influenced by argument strength in content messages and contextual Website features than younger adults. Verbal protocol analysis revealed that older adults tended to accept the facts they read on the Web page instead of further deliberating on their credibility. They also tended to pay less attention to contextual Website features relevant to the credibility of the information. We also found that older adults lower sensitivity to credibility cues on a Web page could at least be partially explained by their declined cognitive ability and lack of Internet experience. On the other hand, health-related domain knowledge was found to be useful in helping older adults to make better credibility judgments.