Coaches influence athletes’ body image, but often feel ill-equipped to address body image concerns and inadvertently perpetuate harmful body ideals. No evidence-based, empirically-tested body image intervention for coaches exists. This study evaluated the acceptability and preliminary efficacy of a novel web-based intervention (body confident coaching [BCC]), comprising five self-led 20-min modules. A pilot randomized controlled trial was conducted with 97 coaches of adolescent girls (M age = 36.6yrs, SD = 10.4; 70% women). Coaches were randomized into the intervention (n = 52) or waitlist control condition (n = 45). Intervention condition participants completed baseline self-assessments (demographics, target outcomes), took part in BCC over two weeks, and completed post-intervention self-assessments (target outcomes, acceptability, adherence). Waitlist control participants completed baseline (demographics, target outcomes) and post-intervention self-assessments (target outcomes), after which they received unmonitored access to the intervention. Intervention condition participants who completed post-intervention assessments (n = 16) finished all five modules and 75% reported engaging with the additional resources. Coaches found the intervention easy to follow, appropriate, useful, and enjoyable. Preliminary efficacy analyses indicated that the intervention condition reported higher levels of self-efficacy toward body image (η p 2 = .19), and lower levels of fat phobia (η p 2 = .39) and gender essentialist beliefs (η p 2 = .20) at post-intervention, compared to the waitlist condition. A limitation of this study is the small sample size and high attrition rate (51%), which may bias results. Following modifications to the intervention and trial protocol, BCC will be evaluated in a large-scale randomized controlled effectiveness trial. Lay summary: Body dissatisfaction is common among girls in sport, but coaches are unprepared and unskilled to address these concerns, and few resources for coaches exist. A new education program was found to be appropriate, useful, and enjoyable for coaches and improved their ability to recognize and address athletes’ body image concerns.