Success of HIV prevention projects for injection drug users (IDUs) depends on the support of the communities in which they are implemented. This article presents data from cross-sectional community surveys of HIV knowledge and attitudes toward peer-based HIV prevention interventions for injection drug users in a border area of Lang Son Province, Vietnam and Ning Ming County, Guangxi Province, China. Analysis of these surveys at baseline and 18 months reveals generally high or improving levels of HIV knowledge and positive attitudes toward the interventions in both Vietnam and China. Levels of knowledge and positive attitudes tended to be higher in Vietnam than in China. Interviews with staff and peer educators suggest that the project's community education efforts have increased support for the interventions and contributed to their smooth implementation. However, the community surveys also reveal some continuing deficits in HIV knowledge and understanding of the interventions, including perceptions that provision of new needles/syringes will result in increased drug use. Additional education, including dissemination of countervailing project data, is necessary to address these deficits and further increase community support for the interventions.