Abstract Introduction Adolescents who evince higher levels of impulsive traits are more susceptible to early use of mature-rated gaming and watching R-rated movies. This is a major public health concern because exposure to mature-rated media in youth is associated with decreased empathy and aggressive behaviors later in life. However, not all youth with higher impulsive traits will be engaged in those risky media activities. Sleep is a critical bioregulatory behavior during adolescence, and shorter sleep duration is associated with decreased emotional regulation and attention span. Yet, few studies examined whether sleep duration moderates the association between impulsivity and risky media usage. Methods The current study examines the associations between sleep, impulsivity, and mature-rated video gaming and movie watching using longitudinal data of 2,757 early adolescents (49.3% female, Mage at 3-year follow-up=12.9 years, SD=0.65), collected through the Adolescent Brain Cognitive Development Study® (2021, release 4.0). The participants’ weighted weekly sleep duration was measured via Fitbit watches for at least seven days at 2-year follow-up. Participants completed questionnaires about impulsivity via UPPS-P Impulsive Behavior Scale at 2-year follow-up and R-rated movie watching and mature video gaming at 2- and 3-year follow-up. Structural equation modeling was conducted in Mplus 8.1 to test impulsivity and sleep duration’s direct and interaction effects on mature media use while controlling for bedtime screen use, parental monitoring, and demographic covariates. Results Higher impulsivity was predictive for more R-rated movie watching (β=0.09, p<.001) one year later. Shorter sleep duration was predictive for more mature video gaming (β=-0.05, p=.006) and R-rated movie watching (β=-0.07, p<.001) one year later. Sleep duration moderates the association between impulsivity and R-rated movie watching (β=-0.04, p=.03). Among youth with high impulsivity, shorter sleep duration was associated with an increased risk for R-rated movie watching. Conclusion Impulsivity is associated with R-rated movie watching, and short sleep duration (objectively measured with Fitbit) in early adolescence partially moderates the association between impulsivity and mature media usage. Sleep duration may be a modifiable factor for prevention and intervention efforts, especially in adolescents at higher risk for excessive mature-rated media usage. Support (if any) National Institutes of Health