Aim To study the effects of pioglitazone on intima-medial thickness(IMT) of carotid artery in type 2 diabetic mellitus(T_2DM) patients.Methods T_2DM patients(n=68) were divided into pioglitazone group(n=34) and placebo group(n=34) by the rule of random and double-blind.The IMT of carotid artery was detected by B-mode ultrasound 3 months later.After 3 months treatment,postprandial blood glucose(PBG),HbA1c,total cholesterol(TC),triglyceride(TG),low density lipoprotein cholesterol(LDLC)and high density lipoprotein cholesterol(HDLC)were measured.Results IMT of carotid artery in pioglitazone group was significantly lower than that in placebo group(p<0.01).Compared with placebo group,the serum levels of PBG,HbA1C and TG in pioglitazone treatment group were significantly lower(p<0.01) and the level of HDLC was markedly increased(p<0.01).No significant difference of TC and LDLC was found between the two groups. The decreased IMT of carotid artery was significantly associated with chang of LDLC and HDLC.Conclusion Pioglitazone could significantly reduce IMT of carotid artery in T_2DM patients and have positive effects on improving vascular complications of T_2DM patients.