Background: Cancer survivors are at increased risk of long-term adverse effects related to the disease or treatment. Thus, it is important for cancer survivors to adopt a health-promoting lifestyle (HPL). This study aims to: (1) describe health behavior self-efficacy (HBSE) and HPL of adolescent survivors of childhood cancer, (2) examine the relationships between HBSE, HPL, and various demographic factors, and (3) identify determinants of HPL among adolescent survivors of childhood cancer. Method: A descriptive cross-sectional study was conducted with adolescent survivors of childhood cancer, ranged in age from 11 to 19 years (n = 82). Participants were recruited from pediatric oncology follow-up clinics at two medical centers in southern Taiwan. Data for each participant were collected from questionnaires assessing HBSE and HPL. Results: Only 61% of the adolescent survivors were considered as normal weight. The exercise was the lowest scoring HBSE subscale. Factors associated with better HPL included: education level, HBSE, well-being, and a healthy diet. Specifically, survivors diagnosed with cancer during adolescence exhibited significantly greater self-efficacy with stress management (F = 3.20, p = .04) compared with those diagnosed at pre-school ages. HBSE scores for well-being and a healthy diet were significant predictors of HPL, accounting for 43.8% of the total variance observed. Discussion: Our findings suggest that the age of diagnosis of childhood cancer significantly modulates the frequency of health-promoting behaviors of adolescent survivors. Thus, interventions designed to enhance adolescents’ well-being and the management of a healthy diet may enhance HPL in survivors of childhood cancer.