Seasonal variation of blood pressure (BP) has been reported in small populations or by BP levels captured at only a few points in a year, for example, summer and winter. We aimed to investigate the multiyear seasonal variation in self-measured home BP among hypertensive patients receiving antihypertensive medications. We selected 1649 eligible patients receiving antihypertensive drug treatment, and weekly averaged home BPs were analyzed throughout the follow-up period. Systolic and diastolic home BPs were fitted with the cosine function: 'Variation+Other Effects+Intercept', in which the 'Variation' was expressed by a cosine curve with three parameters representing: (1) maximum-minimum difference of home BP in one cycle of the cosine curve; (2) time required for one cycle of the cosine curve for home BP variation; and (3) time at which home BP reached the maximum point. Maximum-minimum differences in home BP were 6.7/2.9 mm Hg, and the highest home BPs were observed in mid-to-late January. In the multivariable-adjusted model, a large maximum-minimum difference in home BP was associated with lower body mass index and older age, and larger differences were observed in men compared with women. Summer-winter difference in home BP was essentially similar every year, though it was marginally reduced by 0.14/0.04 mm Hg per year, under long-term antihypertensive treatment. Records of daily home BP measurements enable us to capture long-term factors such as seasonal variation. Home BP should therefore be carefully monitored, particularly in patients with increased BP in winter, to mitigate cardiovascular risk.