Abnormalities in circadian blood pressure (BP) variation have been suggested to be associated with cardiovascular diseases and mortality. Factors affecting this variability need to be clarified to precisely evaluate the risk of circadian BP abnormalities. Given the seasonal differences in casual BP, it was hypothesized that nocturnal BP may also differ by season. Here, we aimed to clarify the seasonality of circadian BP variation, as well as the factors associated with this seasonality, in a large-scale general population (n = 4780). This is a cross-sectional study based on multiday BP values measured in the evening, during sleep, and in the morning. Measurements were taken at home using an automatic cuff-oscillometric device. The sleeping period was objectively defined by actigraphy. The nocturnal systolic BP fall was significantly less in individuals whose BP was measured during the summer season (summer, -5.8 ± 7.8%; middle (spring or autumn), -8.2 ± 7.5%; winter, -11.0 ± 7.7%; p < 0.001), resulting in higher frequencies of riser (summer, 19.9; middle, 12.8; winter, 7.8%) and non-dipper (summer, 51.4; middle, 46.3; winter, 37.0%) patterns in the summer season (p < 0.001). The results of linear regression analysis identified the middle (β = 0.154, p < 0.001) and summer season (β = 0.261, p < 0.001) as strong positive determinants for decreasing the nocturnal SBP fall. No seasonality was observed in day-to-day variability of the dipping pattern (Kendall's coefficient: winter, 0.527; middle, 0.539; summer, 0.515). The nocturnal BP fall was largely different by season, with a higher frequency of riser and non-dipper patterns in the summer. The seasonality might not be due to the seasonal difference in day-to-day variability of nocturnal BP changes.