OBJECTIVES: Little is known about workplace measures against coronavirus disease 2019 (COVID-19) in Japan during the winter of 2020, especially in micro-, small-, and medium-sized enterprises (MSMEs). This study aimed to provide an overview of the current situation of anti-COVID-19 measures in Japanese enterprises during the winter, considering company size. METHODS: This study was an Internet-based nationwide cross-sectional study. Individuals who were registered as full-time workers were invited to participate in the survey. Data were collected using an online self-administered questionnaire in December 2020. The chi-squared test for trend was performed to calculate the P-value for trend for each workplace measure across company sizes. RESULTS: For the 27 036 participants, across company sizes, the most prevalent workplace measure was encouraging mask wearing at work, followed by requesting that employees refrain from going to work when ill and restricting work-related social gatherings and entertainment. These measures were implemented by approximately 90% of large-scale enterprises and by more than 40% of micro- and small-scale enterprises. In contrast, encouraging remote working was implemented by less than half of large-scale enterprises and by around 20% of micro- and small-scale enterprises. There were statistically significant differences in all workplace measures by company size (all P < .001). CONCLUSIONS: We found that various responses to COVID-19 had been taken in workplaces. However, some measures, including remote working, were still not well-implemented, especially in smaller enterprises. The findings suggest that occupational health support for MSMEs is urgently needed to mitigate the current wave of COVID-19.