The theory-driven Electronic Health Information for Life-Long Learners via Collaborative Learning (eHILLL-CL) intervention, developed and tested in public libraries, aims to improve older adults' e-health literacy. A total of 172 older adults participated in this study from August 2009 to June 2010. Significant differences were found from pretest to posttest in general computer/Web knowledge and skill gains and in e-health literacy (p<0.001 in all cases; effect sizes: 0.5–2.1; statistical power: 1.00 even at the 0.01 level) and three attitude measures (p<0.05) for both computer anxiety and attitudes toward the aging experience in physical change, and p<0.01 for attitude toward the CL method; effect sizes: 0.2–0.3; statistical power: 0.4–0.8, at the 0.05 level). No significant difference was found in other variables. Participants were highly positive about the intervention and reported positive changes in health-related behavior and decision making. Group composition (based on gender, prior familiarity with peers, or prior computer experience) showed no significant impact on CL outcomes. These findings contribute to the CL and health literacy literatures and infer that CL can be a useful method for improving older adults' e-health literacy when using the specific strategies developed for this study, which suggests that social interdependence theory can be generalized beyond the younger population and formal educational settings.