Free sex behavior among adolescents increases the risk of unintended pregnancy, sexually transmitted infections, and psychosocial problems. Attractive and easily accessible digital educational media are needed to improve adolescents’ knowledge. This study aimed to analyze the effect of a digital flipbook–based educational medium on adolescents’ level of knowledge about free sex at SMK Negeri 4 Negara. This study used a pre-experimental one-group pretest–posttest design conducted on November 12–14, 2025, with a sample of 22 tenth-grade students. Knowledge was measured using a 20-item questionnaire, and the educational intervention was delivered in one session lasting 20–30 minutes. The results showed that the largest category at pretest was moderate knowledge (72.7%), whereas at posttest the largest category became good knowledge (63.6%). The Wilcoxon test indicated a significant difference in knowledge levels before and after the intervention (Z = -2.848; p = 0.004). Theoretically, presenting information through a combination of text and visuals strengthens attention, comprehension, and retention, thereby facilitating knowledge change. The researchers assumed that the visual appearance, concise content flow, and easy access to the flipbook helped students stay focused and motivated. Conclusion: digital flipbook–based educational media effectively improves adolescents’ knowledge about free sex at SMK Negeri 4 Negara.