Objective · To understand boys’ pubertal timing in school in two urban districts of Chongqing and explore the relationship between pubertal timing and physical activity or sleeping time. Methods · Using a stratified random cluster sampling, 3 403 boy students (10-18 year-old) were selected and completed the physical examination and questionnaire survey. 1 282 participants experiencing first spermatorrhea were chosen as research objects. According to age of first spermatorrhea, the objects were divided into on-time group (964 cases) and later group (318 cases). Results · The composition of weekly high (χ2=11.488, P=0.009), medium (χ2=7.829, P=0.050) physical activity and daily sleeping time (χ2=17.803, P=0.000) in two groups were significantly different. Controlling covariates (age, height and weight), compared with boys in on-time group, later group boys were less likely to engage in 5-7 days (OR=0.596, 95% CI: 0.367-0.967) and 3-4 days (OR=0.590, 95% CI: 0.370-0.941) high physical activity every week, and 9-11h (OR=0.207, 95% CI: 0.088-0.489) sleep every day. Conclusion · The age of first spermatorrhea in boys might be associated with the intensity of weekly physical activity and daily sleeping time.