Older adults' access to healthcare services may have been affected by the COVID-19 pandemic. This study explored the effect of the first wave pandemic on the medical expenditure of older adults in China. Difference-in-Difference models captured both temporal and geographical variation in COVID-19 exposure to estimate the impacts of the pandemic on medical expenditure through a quasi-natural experiment. Data derived from the China Family Panel Studies. Results indicate that exposure to the pandemic significantly decreased total medical expenditures, hospital expenditures, and non-hospital medical expenditures of Chinese older adults by 15% (95% CI 12%-17%), 5% (95% CI 2%-7%), and 15% (95% CI 13%-16%), respectively, for each standardized severity increment. Females, less well-educated people, and individuals without internet access were most susceptible to experiencing these reductions. This study revealed that COVID-19 exerted a detrimental influence on the medical expenditure of older adults in mainland China. The "hidden epidemic" of non-COVID-19 medical needs of older adults deserves more attention on the part of policymakers.