Objective Adolescents with frequent (versus infrequent) social media use display higher cannabis use prevalence. This study examined associations of social media use frequency with pro-cannabis attitudes, an actionable intervention target. Methods Youth aged 13-17 in Oklahoma, United States completed an online, cross-sectional survey (March-October 2023) measuring social media use frequency (0-1.5 vs. 1.5+ hours/day), pro-cannabis attitudes (e.g., "cannabis is an effective treatment for mental health problems"), past-month cannabis use (yes/no), and individual characteristics (e.g., age, tobacco use). Regression models tested associations of social media use frequency with pro-cannabis attitudes, pro-cannabis attitudes with past-month cannabis use, and social media use frequency with past-month cannabis use. Results The sample (N = 409; 53.8 % female) was 58.7 % non-Hispanic [NH] White; 68.5 % used social media >1.5 hours/day; 22.7 % reported past-month cannabis use, and cannabis attitudes averaged 3.2 (SD = 1.0; 1 = less positive, 5 = more positive). In models adjusted for sex, gender, age, family finances, mental health symptoms, tobacco use, alcohol use, offline cannabis marketing exposure, and cannabis-related social media content exposure, participants endorsing more frequent social media use had greater pro-cannabis attitudes (B = 0.24, SE = 0.10; p = .020). Pro-cannabis attitudes were, in turn, associated with greater odds of past-month cannabis use (aOR = 1.80, 95 % CI [1.28, 2.55]). Social media use frequency was not directly associated with past-month cannabis use (p = .344); however, past-month cannabis use prevalence was descriptively higher among youth with frequent (24.3 %) versus infrequent (19.4 %) social media use. Conclusions Adolescents with frequent social media use may develop pro-cannabis attitudes, which may be associated with future cannabis use. Prevention messaging could target attitudes.