Adolescent girls are at substantial risk of sexually transmitted diseases including HIV. To reduce these risks, we developed Health Education And Relationship Training (HEART), a web-based intervention focused on developing sexual assertiveness skills and enhancing sexual decision-making. This study assessed the feasibility and acceptability of this new program and examined if perceived acceptability varied according to participant ethnicity, sexual orientation or sexual activity status. Participants were part of a randomized controlled trial of 222 10th-grade girls (Mage = 15.26). The current analyses included those in the intervention condition (n = 107; 36% white, 27% black and 29% Hispanic). HEART took approximately 45 min to complete and was feasible to administer in a school-based setting. Participants found the program highly acceptable: 95% liked the program and learned from the program, 88% would recommend the program to a friend and 94% plan to use what they learned in the future. The primary acceptability results did not vary by the ethnicity, sexual orientation or sexual activity status of participants, suggesting broad appeal. Results indicate that this new online program is a promising method to reach and engage adolescents in sexual health education.