Objective To investigate the relationships of blood pressure circadian rhythm and brain natriuretic peptide (BNP) with left ventricular hypertrophy (LVH) in patients with primary hypertension. Methods Totally 349 patients (74 with LVH and 275 without LVH) with primary hypertension were enrolled in this study.Echocardiography was performed to determine left ventricular mass index (LVMI) using the Devereux formula. The nocturnal blood pressure decline rate,24-hour blood pressure (24 h PP; especially 24 h mean systolic blood pressure,24 h SBP) and blood pressure index (PPI) were determined by 24 h-ambulatory blood pressure monitoring. These 349 hypertensive patients were divided into four groups including supper-dipper group (defined as≥;20%, n=7),dipper group (defined as 10%- 20%, n=77),non-dipper group (defined as 0- 10%, n=173),and anti-dipper group (defined as<0, n=92). The baseline demographic characteristics of patients were collected. Fasting blood sugar,blood lipids,blood urea nitrogen,serum cretinine,cystatin C,uric acid,and plasma BNP level were measured. Results The patients with LVH (n=74) had significantly higher percentage of grade 3 hypertension (85.1% vs. 46.9%;χ2=34.428,P<0.001),24 h SBP (134 mmHg vs. 129 mmHg; t=3.175,P=0.002)(1 mmHg=0.133 kPa),daytime-mean SBP (134 mmHg vs. 130 mmHg; t=2.197,P=0.029),night-mean SBP(132 mmHg vs. 121 mmHg; t=4.763,P<0.001),and 24 h PP(57 mmHg vs. 52 mmHg; t=4.120,P<0.001) and PPI (0.43 vs. 0.41; t=3.335,P=0.001) and lower nocturnal blood pressure decline rate [(1.30±8.02)% vs. (5.68±7.25)%; t=-4.510,P<0.001] than the non-LVH patients (n=275). The LVH hypertensive group had significantly higher BNP level (87.8 pg/ml vs. 28.8 pg/ml; t=2.170,P=0.034) and LVMI (135.1 g/m2 vs. 88.7 g/m2; t=15.285,P<0.001) than the control group. No significant difference was observed in the BNP level among supper-dipper,dipper,non-dipper and anti-dipper groups (P=0.137).However,the difference was statistically significant in the LVMI (P=0.001). Additionally,patients in the anti-dipper group had significantly higher LVMI than those in the dipper patients (100.3 g/m2 vs. 86.3 g/m2; t=4.335,P<0.001) and non-dipper (100.3 g/m2 vs.93.7 g/m2; t=1.987,P=0.048). Patients in the non-dipper group had significantly higher LVMI than those in the dipper group (93.7 g/m2 vs. 86.3 g/m2; t=2.693,P=0.008). The multivariate linear correation analysis and logistic regressions analysis suggested a significant correlation of LVMI with BNP and the grade of hypertension. Conclusion With the increasing of plasma BNP level,the left ventricular hypertrophy is closely related to abnormal blood pressure circadian rhythm and the grade of hypertension in primary hypertensive patients.