Background: The question to involve or restrict medical students’ involvement in the coronavirus disease 2019 (COVID-19) pandemic response remains contentious. As their state of preparation and perceptions in volunteering during this pandemic have yet to be investigated, this study aims to evaluate Indonesian medical students’ willingness to volunteer and readiness to practice during the COVID-19 pandemic. Methods: A web-based survey was conducted among undergraduate medical students throughout Indonesia. Socio-demographic and social interaction information, in addition to willingness to volunteer and readiness to practice, were obtained using a self-reported questionnaire. The significance level was set at 5%. Results: Among 4870 participants, 2374 (48.7%) expressed their willingness to volunteer, while only 906 (18.6%) had adequate readiness to practice. Male students, students with prior volunteering experience in health or non-health sectors, and students from public universities or living in Central Indonesia (vs Java) had higher scores of willingness and readiness to volunteer. Students from Sumatra also had better preparedness (odds ratio [OR] 1.56, 95% confidence interval [CI] 1.15–2.12, p = 0.004), while the opposite occurred for students from Eastern Indonesia (OR 0.63, 95% CI: 0.44–0.89, p = 0.002)–when compared to students from Java. In addition, compared to students with high family income, students from lower-middle income families were less willing to volunteer (OR 0.76, 95% CI: 0.59–0.98, p = 0.034), though those with low family income had better readiness (OR 1.51, 95% CI: 1.10–2.08, p = 0.011). Shortage of medical personnel, sense of duty, and solicitation by stakeholders were the main reasons increasing the students’ willingness to volunteer; whereas contrarily fear for own’s health, absence of a cure, and fear of harming patients were the primary factors diminishing their willingness to volunteer. Conclusion: Our findings indicated that many Indonesian medical students are willing to volunteer, yet only few of them were ready to practice, indicating that further preparations are required to maximize their potentials and minimize their exposure to hazards. We suggest that their potentials as a firm support system during the pandemic should not be overlooked, and that the integration of relevant courses to the medical curricula are imperative to prepare for future public health emergencies. © 2021, The Author(s).