Abstract: Objective To investigate the correlations of serum 25-hydroxyvitamin D 25（OH）Dlevel with blood pressure variability（BPV）and circadian rhythm in essential hypertensive patients. Methods Serum 25（OH）D concentrations were detected in 389 patients with untreated essential hypertension. According to the serum 25（OH）D level,all patients were divided into normal（＞30nmol/L,n=89）,mild deficiency（16-30nmol/L,n=120）and severe deficiency（＜16nmol/L,n=180）group. The 24-hour ambulatory blood pressure monitoring was performed on all patients. The mean systolic and diastolic blood pressure in the periods of 24-hour,daytime and nighttime and the corresponding standard deviations（as BPV）were recorded. The relationships of the level of serum25（OH）D with BPV and circadian rhythm were analyzed. Results Among these patients with hypertension,those with normal 25（OH）D level,mild 25（OH）D deficiency,severe 25（OH）D deficiency accounted for 22.9%,30.8%,46.3%,respectively. The mean concentration of 25（OH）D was lower in female than that in male（15.20±8.23）vs（19.47±7.02）nmol/L,P＜0.05. Among the 3groups,there were statistical differences in mean 24-hour systolic blood pressure（24hSBP）,mean daytime systolic blood pressure（dSBP）,mean nighttime systolic blood pressure（nSBP）,24-hour systolic blood pressure standard deviation（24hSSD）,24-hour diastolic blood pressure standard deviation（24hDSD）,daytime systolic blood pressure standard deviation（dSSD）,daytime diastolic blood pressure standard deviation（dDSD）,nighttime systolic blood pressure standard deviation（nSSD）,nighttime diastolic blood pressure standard deviation（nDSD）and the decline rate of nighttime systolic and diastolic blood pressure（all P＜0.05）. Compared with normal 25（OH）D group and mild 25（OH）D deficiency group,mean 24-hour diastolic blood pressure（24hDBP）,mean daytime diastolic blood pressure（dDBP）,mean nighttime diastolic blood pressure（nDBP）were higher in severe 25（OH）D deficiency group（all P＜0.05）. While there was no differences between normol25（OH）D group and mild 25（OH）D deficiency group（P＞0.05）. Pearson correlation analysis indicated that the serum 25（OH）D level was negatively correlated with 24 hSSD,24hDSD,dSSD,dDSD,nSSD,nDSD（r=-0.583,-0.530,-0.520,-0.389,-0.463,-0.377,respectively,all P＜0.01）and positively correlated with the decline rate of nighttime systolic and diastolic blood pressure（r=0.308,0.336,respectively,all P＜0.01）. Multiple linear regression analysis showed that 25（OH）D was an influencing factor for 24hSSD（B=-0.227）,24hDSD（B=-0.193）,dSSD（B=-0.211）,dDSD（B=-0.119）,nSSD（B=-0.193）,nDSD（B=-0.136）and the decline rate of nighttime systolic and diastolic blood pressure（B =0.273,0.329,respectively）（all P ＜0.01）.Conclusion Serum 25（OH）D may be an influencing factor for BPV and circadian rhythm changes in patients with essential hypertension.