Objective: To explore the relationship between non-dipper pattern of blood pressure circadian rhythm and homocysteine (Hcy), carotid atherosclerosis (CAS) in patients with type 2 diabetes mellitus (T2DM). Methods: A total of 240 T2DM patients including 139 male and 101 female were enrolled. According tonocturnal blood pressure falling rates, the patients were divided into 2 groups: Dipper group,n=80 and Non-dipper group,n=160; based on CAS condition, the patients were divided into another set of 2 groups: CAS group,n=119 and Non-CAS group,n=121. Blood levels of Hcy, carotid intima media thickness (CIMT) and 24hSBP, dSBP, nSBP, 24hDBP, dDBP, nDBP were compared between 2 groups in each set; the risk factors of CAS were analyzed. Results: The following indexes were higher in Non-dipper group than Dipper group: Hcy by μmol/L (16.41.0±8.08 vs 12.55±4.07), CIMT by mm (1.00±0.59 vs 0.80±0.30), 24 hSBP by mmHg (138.7±19.2 vs 127.5±15.6), dSBP (139.4±19.2 vs 132.0±16.2), nSBP (136.4±20.0 vs 113.8±15.0), nDBP (74.0±12.0 vs 64.9±9.8), allP<0.01. Multi linear regression analysis indicated that Hcy (β=0.011,P<0.01), nSBP (β=0.021,P<0.01), nDBP (β=0.018,P<0.01) could affect blood pressure circadian rhythm. The following indexes were higher in CAS group than Non-CAS group: CIMT (1.18±0.65 vs 0.69±0.72), age by years (62.33±12.02 vs 59.17±10.80), 24 hSBP (138.2±18.2 vs 131.9±18.9), dSBP (139.5±18.4 vs 134.4±18.5), nSBP (133.9±20.7 vs 123.9±20.9) nDBP (73.3±12.8 vs 68.6±11.0),P<0.05 orP<0.01; while 2 indicators in CAS group were lower than Non-CAS group: SBPF (4.00±7.89 vs 7.66±7.36), DBPF (5.95±8.44 vs 10.19±8.67),P<0.01. Logistic regression analysis showed that age (OR=2.204,P<0.05), nDBP (OR=2.357,P<0.05), SBPF (OR=2.562,P<0.01) were the risk factors for carotid atherosclerosis. Spearman correlation analysis presented that CIMT was positively related to age (0.195,P<0.05) and negatively related to SBPF (r=-0.191,P<0.01). Conclusion: T2DM patients with non-dipper pattern of blood pressure circadian rhythm were usually combining high blood level of Hcy, non-dipper pattern was the independent risk factor for CAS. Restoring blood pressure circadian rhythm is important to prevent atherosclerosis.