Objectives: To assess (1) the willingness to get a COVID-19 vaccine among Medicare beneficiaries, (2) the associated factors, and (3) the reasons for vaccine hesitancy. Methods: Data were taken from the Medicare Current Beneficiary Survey (MCBS) 2020 Fall COVID-19 Supplement, conducted October-November 2020. Willingness to get a COVID-19 vaccine was measured by respondents' answer to whether they would get a COVID-19 vaccine when available. We classified responses of "definitely" and "probably" as "willing to get," and responses "probably not," "definitely not," and "not sure" as "vaccine hesitancy." Reasons for vaccine hesitancy were assessed by a series of yes/no questions focusing on 10 potential reasons. The analytical sample included 6715 adults 65 years and older. We conducted a logistic regression model to assess demographic factors and other factors associated with the willingness to get a COVID-19 vaccine. All analyses were conducted in Stata 14 and accounted for the complex survey design of MCBS. Results: Overall, 61.0% (95% confidence interval [CI], 59.1-63.0) of Medicare beneficiaries would be willing to get a vaccine when available. Among those who were hesitant, more than 40% reported that mistrust of the government and side effects as the main reasons. Logistic regression model results showed that non-Hispanic Blacks (adjusted odds ratio [AOR] = 0.33; 95% CI, 0.24-0.44) and Hispanics (AOR = 0.60; 95% CI, 0.47-0.77) were less willing to get a vaccine than non-Hispanic Whites; beneficiaries with an income of less than $25 000 (AOR = 0.71; 95% CI, 0.62-0.81) were less willing to get the vaccine than those with an income of $25 000 or more; those who did not think that the COVID-19 virus was more contagious (AOR = 0.53; 95% CI, 0.41-0.69) or more deadly (AOR = 0.51; 95% CI, 0.41-0.65) were also less willing to get the vaccine than those who thought that the virus was more contagious or more deadly than the influenza virus. Conclusions: The 2020 MCBS survey data showed that close to 40% of Medicare beneficiaries were hesitant about getting a COVID-19 vaccine, and the hesitancy was greater in racial/ethnic minorities. Medicare beneficiaries were concerned about the safety of the vaccine, and some appeared to be misinformed. Evidence-based educational and policy-level interventions need to be implemented to further promote COVID-19 vaccination.