We examined effects of self-care after school hours and psychosocial factors on cigarette smoking and alcohol use among adolescents in China. Survey data were obtained from 4734 7th and 11th grade students from seven cities across China. Students were queried about the frequency and quantity of unsupervised self-care after school in an average week. Tobacco and alcohol usage were also obtained. Odds ratios were calculated to determine the strength of association between unsupervised self-care after school and substance use. Results indicated that the amount of self-care after-school (how many days and how many hours per week) was significantly associated with increased risk for smoking and alcohol use among Chinese adolescents. These associations remained significant even after controlling for anxiety, depressive symptoms, and peer influence. The interaction between unsupervised self-care after school and peer influence indicated that unsupervised self-care after school is a stronger risk factor for smoking among adolescents with pro-smoking friends. The findings suggest that substance use prevention programs for youth in China should try to enhance parental monitoring. As it may not be feasible for families to revert to a lifestyle that includes supervision by relatives, other approaches such as organized after-school care are worthy of consideration.