Abstract: Objective: To investigate the role of soy isoflavones(SI) in preventing and treating myocardial injury of experimental diabetic rats.Methods: Forty eight SD rats were randomly divided into six groups:normal control group(NC),diabetic control group(DC),three SI treatment groups(L SI,M SI,H SI) and nilestriol treatment group(NT).All the rats were given streptozotocin(STZ) intraperitoneal injection(ip) except NC group rats,and the dosages were all 50 mg/kg.After 4 weeks,SI 30,60,120 mg·kg^-1·d^-1 were given in L SI,M SI,H SI groups,nilestriol 0.2 mg·kg^-1·wk^-1 was given in NT group,and natural salutions were given in NC and DC groups.Volumes in all groups were 2 ml·kg^-1·d^-1.Drugs were all orally administered using stomach tubes.The level of body weight(BW) and blood glucose(BG) were measured.LDH,CK,SOD activities and MDA contents in myocardical tissue were also measured.Results: Compared with DC group,LDH,CK,SOD activities in myocardial homogenate and the level of BW were significantly increased in H SI group(P<0.05 to P<0.01).Conclusions: High does soy isoflavones can increase LDH,CK,SOD activities in myocardial homogenate and the level of BW in diabetic rats.