Background: The aim of this study was to clarify the impact of limitations of activity due to the COVID-19 pandemic on diabetes management.Methods: To clarify the impacts of the emergency declared on April 7 2020, 345 patients, 1109 patients, and 752 patients whose HbA1c levels were measured in both March and April, May, or June were selected. The patients to be compared were selected from the 2019 data under the same conditions. In 2019, 469 patients, 1315 patients, and 783 patients whose HbA1c levels were measured in both March and April, May, or June were selected. The impact of restricted activity on diabetes management due to the declared emergencies was assessed by comparing HbA1c levels in April, May, and June minus the HbA1c levels in March of both 2019 and 2020. Subjects with a difference in HbA1c levels greater than 0 were defined as “worsened”, and subjects with a difference in HbA1c levels less than or equal to 0 were defined as “improved”. The deterioration rate and the improvement rate of the HbA1c level in 2019 and 2020 were compared by the Chi-squared test. Second, the linear trends of HbA1c from April to June between 2019 and 2020 were calculated by mixed model repeated measures ANOVA.Results: There were more patients with worsening HbA1c levels from March to April in 2020 than in 2019: 122 (26.0%) vs. 137 (39.7%), p<0.01. There were more patients with improved HbA1c levels from March to June in 2020 than in 2019: 478 (61.0%) vs. 512 (68.1%), p<0.01. Patients with improved HbA1c levels between March and May showed no significant difference between 2020 and 2019: 814 (61.9%) vs. 713 (64.3%), p=0.23. Slopes of HbA1c levels from April to June in 2019 and 2020 were -0.0024 (-0.0039, -0.0009) and -0.0099 (-0.0117 -0.0081), respectively. There were significant differences in the slopes -0.0075 (-0.0097, -0.0053), p<0.01) between the years.Conclusions: HbA1c levels did not appear to show persistent deterioration during the observational period in 2020. Meanwhile, some diabetic patients may have shown both improved and worsened diabetes control during the COVID-19 pandemic.