Objective: During the COVID-19 pandemic, vaccine hesitancy and low awareness of heightened risks became evident, also among high-risk groups like individuals with mental disorders. This study investigated the effectiveness of an educational video designed to improve COVID-19 vaccine acceptance among individuals with mental disorders. Methods: A randomized online experiment was conducted with n = 639 participants (MAge = 37.04 [SD = 14.85], 77.8% female) from the German general population in 2022. Participants were randomly assigned to either an educational video about COVID-19 vaccination and its particular importance for individuals with mental disorders, or a control group (no video). Key outcomes included vaccination willingness, disease-related threat perceptions and COVID-19 vaccine-specific evaluations. Moderation analyses examined differential effects for diagnostic status and internalizing psychopathology. Results: The intervention significantly increased awareness of the importance of COVID-19 vaccination for individuals with mental disorders (p = .033, d = 0.17), perceived severity of COVID-19 (p = .010, d = 0.21), and calculative considerations of decision-making (p = .015, d = 0.19). However, the intervention did not significantly improve vaccination willingness or vaccine-specific beliefs (ps > .05). Moderation analyses showed that participants with a self-reported mental disorder showed enhanced perceived susceptibility (p = .032, d = 0.36), while no effect was observed for participants without a mental disorder. Conclusions: The video-based intervention effectively improved awareness and disease-related threat perceptions. However, the absence of significant changes in vaccination willingness and vaccine-specific evaluations highlights the need for strategies that more effectively address vaccine hesitancy.