Aim To investigate the relationship between ambulatory arterial stiffness index（AASI） and microalbuminuria （MAU） and circadian rhythm in patients with primary hypertension. Methods A total of 120 patients with primary hypertension were enrolled . Ambulatory blood pressure monitoring（ABPM） was performed for AASI. Serum lipids profile , Serum creatinine and blood urea nitrogen were detected. Glomerular filtration rate（GFR） was estimated by simplified MDRD equation. Urinary albumin and creatinine concentrations were determined on a morning spot-urine sample. AASI was defined as one minus the regression slope of diastolic on systolic blood pressure. MAU was defined as urinary albumin-creatinine ratio （ACR） of at least 22 mg/g in males or of 31 mg/g in females. Nocturnal non dip ping referred to a 10% or lesser magnitude reduction in mean artery pressure（MAP）at nighttime compared to daytime MAP average values,the remainder was defined as dipper. The subjects were divided into four groups according to AASI in quartile: AASI≤0.34（n43）, 0.34＜AASI≤0.46（n44）, 0.46＜AASI≤0.56（n40） and AASI＞0.56（n40） group. The differences between the four groups were compared. According to ACR,patients were divided into MAU group（n68） and non-microalbuminuria （NMAU） group（n99）. The subjects were divided into dipper group（n63） and non-dipper group （n104）according to nocturnal MAP fall rate . The association between AASI , MAU and circadian rhythm of blood preasure were analysed. Results ⑴With the AASI increased，the patients had higher urinary ACR and 24hSBP、24hDBP and 24hPP（P<0.05）,and lower GFR level and dipper hypertension ratio（P<0.05）. （2）AASI in hypertension patients with Microalbuminuria（0.58±0.11） was significantly higher than those of the non-microalbuminuria （0.28±0.12）group, （P<0.05）. Significant independent correlations were revealed between AASI and age（β0.369, P<0.001） and logACR（β0.566, P<0.001）according to multivariate regression analysis. （3）AASI in hypertension patients with non-Dipper type（0.54±0.13） was significant higher than those of Dipper type（0.33±0.14） （P<0.05）,Multiple Logistic regression analysis showed AASI,MAU,age,are the independ risk factors for abnormal circadian blood preasure，the odds ratios were 1.491,1.278,1.246 . Conclusion The increase of AASI is associated with MAU and Non-dipper rhythm in patients with primary hypertension.