BACKGROUND: The World Health Organization recommends all men who have sex with men (MSM) receive Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV) testing. MSM in China are a high-risk group for HBV and HCV infection, but test uptake is low. Crowdsourcing invites a large group to solve a problem and then shares the solution with the public. This nationwide online randomized controlled trial will evaluate the effectiveness of a crowdsourced intervention to increase HBV and HCV testing among MSM in China. METHODS: Seven hundred MSM will be recruited through social media operated by MSM organizations in China. Eligible participants will be born biologically male, age 16 years or older, report previous anal sex with another man, and reside in China. After completing a baseline online survey, participants will be randomly assigned to intervention or control arms with a 1:1 allocation ratio. The intervention will include two components: (1) a multimedia component will deliver two videos and two images promoting HBV and HCV testing developed through a crowdsourcing contest in China; (2) a participatory component will invite men to submit suggestions for how to improve crowdsourced videos and images. The control arm will not view any images or videos and will not be invited to submit suggestions. All participants will be offered reimbursement for HBV and HCV testing costs. The primary outcome is HBV and HCV test uptake confirmed through electronic submission of test report photos within four weeks of enrolment. Secondary outcomes include self-reported HBV and HCV test uptake, HBV vaccination uptake, and change in stigma toward people living with HBV after four weeks. Primary and secondary outcomes will be calculated using intention to treat and as-exposed analyses and compared using two-sided 95% confidence intervals. DISCUSSION: Few previous studies have evaluated interventions to increase HBV and HCV testing in middle-income countries with a high burden of hepatitis. Delivering a crowdsourced intervention using social media is a novel approach to increasing hepatitis testing rates. HBV and HCV test uptake will be confirmed through test report photos, avoiding the limitations of self-reported testing outcomes. TRIAL REGISTRATION: NCT03482388 (29 March 2018).