Objective To study seasonal variation of blood pressure (BP) in patients with essential hypertension (EH) and its association with meteorological elements. Methods In total, 1800 patients with essential hypertension were recruited by cluster sampling from three townships and towns in Qingzhou,Shandong province, 1155 men and 645 women, with an average age of 61.3 years (ranging from 29 to 85years). BP was measured for all of them in sitting position at 8:00 in the morning every seven to 14 days during July 2008 to June 2009. Local meteorological data were collected accordingly such as temperature,humidity and atmospheric pressure, and multivariate regression analysis was performed to show their association. Results In general, BP in patients with EH presented a decreasing trend during the first half year of observation, with the lowest in the summer ( May to August). From September to October, their BP began to increase gradually, and reached the peak in the winter ( November to February nest year). There was significant difference in systolic BP (SBP) and diastolic BP (DBP) between various seasons (Pspring-summer = 0.002 and 0.000, Pwinter-spring = 0.001 and 0.000, Psummer-autumn = 0.045 and 0.000,Psummer-winter =0. 000 and 0. 000, Pautumn-winter =0. 000 and 0. 000, respectively), except for those between the spring and autumn. Both SBP and DBP reversely associated with outdoor air temperature and room temperature(beta= -0.08, t = -2.39, P ＜0.05 and beta = -0.24, t = -6.21, P ＜0.01,respectively), (beta = -0.08, t = -2.39, P ＜0.05 and beta = -0.24, t = -6.21, P ＜0.01,respectively). Conclusions BP in patients with EH reveals seasonal variation, with the lowest in the summer and the highest in the winter and evident fluctuation in the spring and autumn, especially in SBP,which associates with room temperature and their blood vessel elasticity.