Objective：This study aims to investigate the correlation between serum 25-hydroxyvitamin D3［25（OH）D3］ level and carotid atherosclerosis（CAS） in patients with type 2 diabetes mellitus（T2DM）. Methods：The clinical information of 345 patients with T2DM were collected. According to carotid artery color Doppler ultrasound results，the patients were divided into two groups：T2DM with or without atherosclerosis（T2DM-CAS，T2DM-NCAS）. There were 131 normal samples without T2DM nor CAS enrolled as control group. The serum 25（OH）D3 and other biochemical parameters were measured. Results：There was no significant difference in the level of serum 25（OH）D3 between T2DM group and control group. In the male T2DM patients，the serum 25（OH）D3 was significantly lower in T2DM-CAS than in T2DM-NCAS and acted as an independent impact factor for CAS by binary logistic regression analysis. However，for female T2DM patients，CAS was only related to age and pulse pressure. There was no correlation between the level of serum 25（OH）D3 and age in T2DM patients. Conclusion：There was no significant difference in the serum 25（OH）D3 level between the T2DM patients and control. For the male T2DM patients，the serum 25（OH）D3 reduction is a risk factor for CAS.