ObjectiveTo investigate the positive rate of thyroid peroxidase antibody(TPO-Ab) in the diabetic in-patients. MethodsThe positive rates of thyroid peroxidase antibody ( TPO-Ab ) was measured in 1884 subjects, including 1508 type 2 diabetes mellitus ( T2DM ), 76 classic typetype 1 diabeties( T1 DM ), 44 latent autoimmune diabetes in adults (LADA) and 256 "untype" diabetics ( NTDM ). Clinical data were registered and analyzed. Results( 1 )The positive rates of TPO-Ab were 14. 59％ in T2DM(220/1508) ,42. 11％ in T1DM (32/76) ,31.25％ in NTDM ( 80/256 ), 63.64％ in LADA group ( 28/44 ), respectively. The positive rate of T2DM was significantly lower than that of LADA ( P ＜ 0. 05 ), but no significant difference was found in the coparison between T1 DM and NTDM ( P ＞ 0. 05 ). ( 2 ) There were no significant differences between LADA and NTDM groups in the comparison of age, course of disease and BMI ( Ps ＞ 0. 05 ). Conclusion①The positive rate of TPO-Ab in NTDM was significantly higher than that of T2DM, whereas significantly lower than that of T1 DM and LADA.②The positive rate of TPO-Ab was highest in LADA, which indicate that LADA and AIT might have the common etiological mechanisms. ③There is a consisted increasing trend in the positive rate of TPO-Ab from T2DM ,NTDM,and classic T1DM to LADA.