Background: Crowdsourcing may be an effective strategy to develop test promotion materials. We conducted an online randomized controlled trial (RCT) to evaluate a crowdsourced intervention to promote hepatitis B virus (HBV) and hepatitis C virus (HCV) testing among men who have sex with men (MSM) in China. Methods: MSM never previously tested for hepatitis were recruited through social media. Eligible men were randomized to receive an online crowdsourced intervention or no testing promotion materials. Outcomes including self-reported and confirmed HBV and HCV test uptake were assessed after four weeks. Odds ratios (OR) with 95% confidence intervals (95% CI) of men achieving primary and secondary outcomes between the intervention and control arms were calculated. Findings: 556 eligible men were enrolled. Overall, 17•4% (97/556) of men self-reported HBV and HCV testing and 7•9% (44/556) confirmed HBV and HCV test uptake. The intervention was seen by 72•1% and 29•0% of men in the intervention and control arms, respectively. In intention-to-treat analysis, confirmed HBV and HCV test uptake was similar between the two arms, both when using a missing=failure approach (OR 0•98, 95% CI 0•53–1•82) or multiple imputation (OR 1•46, 95% CI 0•72–2•95). Interpretation: This RCT extends the literature by developing and evaluating an intervention to spur hepatitis testing in a middle-income country with a high burden of hepatitis. Overall test uptake among MSM in China was similar to previous interventions promoting hepatitis testing in high-income countries. We found frequent intervention sharing, complicating interpretation of the results, and the role of crowdsourcing to promote hepatitis testing remains unclear.