Objective To explore the association between CRP and circadian variation of blood pressure in both hypertensive and normotensive old population.Methods The 82 patients with essential hypertension (EH) and 79 normotensive adults were enrolled in this study. Serum high sensitive CRP (hsCRP) level was tested by fluorescence immunoassay technology. The 24-hour ambulatory monitor of the level and variability of blood pressure was carried out. Multivariable linear regression models were run to adjust the age, gender, body mass index, blood sugar, blood fat,smoking history and baseline blood pressure for analyzing the association between hsCRP and circadian variation of blood pressure.Results ( 1 ) The variability of systolic blood pressure during daytime,nighttime and 24-h our periods were higher in EH group than in control group (P＜0.01 or P＜0. 05), the variabilities of diastolic blood pressure were also significantly higher than in control group (P＜0. 05), the dipping ratios of nocturnal systolic, diastolic and mean artery pressure were all less than in contrast group (all P＜0.05). (2) The hsCRP was obviously higher in EH group than in control group [(5.44± 1.78)mg/L vs. (3.03±0. 72) mg/L, P＜0. 01]. (3) The hsCRP had positive associations with diastolic blood pressure variability during daytime (r= 0. 492, P＜0. 001 ), nighttime (r=0.240, P=0.048), and 24-hour (r=0.271, P=0.030). The variability in diastolic blood pressure predic ted the level of hs CRP(r=0.660, R2=0.436, P＜0.001). (4) In control group, no significant association was found between CRP and variation of blood pressure.Conclusions The BP variability and serum CRP in EH patients are obviously higher than in normotensive patients,however, the nocturnal BP dipping ratio is less than in normotensive patients. Furthermore, the level of serum hsCRP in EH patients is positively associated with the variation of blood pressure, especially for variation of diastolic blood pressure.