OBJECTIVES: To explore the information sources and knowledge on infant vaccinations of pro-vaccination community members and anti- accination community members on the internet. METHODS: An online survey of 245 parents from three pro-vaccination communities and 92 parents from one antivaccination community was conducted from June 7 to June 23, 2006. RESULTS: Parents from pro-vaccination communities usually gained the information regarding vaccination efficacy and risk mainly from healthcare providers (49.8%) and mass media (47.7%). Pro-vaccination community members considered healthcare providers as the most credible sources of information on vaccination, whereas the anti-vaccination community members usually gained their information regarding vaccine efficiency and risk from Internet child-care cafes and online vaccination communities. Parents of the anti-vaccination community considered the internet as the most credible information source (77.6% for efficacy, 94.8% for risk). In addition, the major reason why anti-vaccination community members didn't vaccinate and, will not vaccinate, was concern about possible side effects of the vaccine. The knowledge level on infant vaccination, education and economic status was higher in the anti-vaccination community. CONCLUSIONS: On-line communities concerned with vaccination are getting popular. The influence of antivaccination parents on the Internet is expected to be high. The government and healthcare providers need to increase their efforts to improve the credibility of information about vaccination. Our findings suggest that online communication regarding vaccinations needs to be considered as a means to increase vaccination rates.