Purpose: This study analyzed the current status of face mask usage. It also identified factors related to the knowledge and behavior regarding the same among older adults living alone during the COVID-19 pandemic. Methods: This descriptive study was conducted via a telephone survey involving 283 older adults living alone in S City from March to April 2020. Knowledge and behavior pertaining to face mask usage were measured using Hilda Ho’s Face Mask Use Scale; reliability of the measurement was Kuder-Richardson formula-20 = .62, Cronbach’s α = .92. Data were analyzed using descriptive analysis, independent t-test, Pearson’s correlation coefficient, and multiple linear regression. Results: Older adults used one mask for 3.55 days on an average. The knowledge level was 9.97 (± 1.84) out of 12 and behavior level was 15.49 (± 1.55) out of 16. Level of education (β = - .31, p < .001), living region (β = .13, p = .017), personal income (β = .12, p = .041) significantly affected the face mask usage-related knowledge, and living region (β = .15, p = .010) significantly affected the face mask usage-related behavior. Conclusion: Older adults living alone are aware of the effects of using face masks. However, their mask usage is inappropriate, for example, the prolonged use of the same mask. Considering the low level of face mask usage-related knowledge, it is necessary to develop customized education programs and infectious disease prevention strategies for older adults possessing low educational levels living alone in urban-rural complex areas.