Misinformation related to coronavirus disease 2019 (COVID-19) has the potential to suppress preventive behaviors that mitigate the spread of COVID-19. Early research on the behavioral consequences of COVID-19 misinformation is mixed, and most rely on cross-sectional data. We examined whether believing in COVID-19 misinformation at one time point influences engaging in preventive behaviors later. In addition, we investigated the role of trust in institutions. We conducted a two-wave survey in South Korea and examined the association between belief in COVID-19 misinformation at Wave 1 and preventive behaviors at Wave 2 controlling for preventive behaviors at Wave 1. We also analyzed whether there is an interaction between belief in COVID-19 misinformation and trust in institutions. Belief in COVID-19 misinformation at Wave 1 significantly increased avoidance of preventive behaviors at Wave 2, but after accounting for trust in institutions, this effect disappeared. Rather, trust in institutions significantly decreased avoidance of preventive behaviors. In addition, misinformation increased avoidance of preventive behaviors among those who trusted institutions the most. Results suggest that building trust in institutions is essential in promoting COVID-19 preventive behaviors. Belief in COVID-19 misinformation may have harmful effects, but these effects were pronounced for those who highly trust institutions.