OBJECTIVE To explore the effects of fasting on blood biochemistry, blood cells, blood electrolyte and and plasma prothrombin time of SPF SD rats.METHODS Fourty SPF SD rats were adaptive breeding for 90 d Serum alanine transaminase(ALT) ,aspartate transaminase(AST), alkaline phosphatase(ALP), creatine kinase (CK), total protein (TP), Albumin, total cholesterol (CHO), triglycerides (TG), glucose (GLU), creatinine (Crea), total bilirubin (TBIL), urea nitrogen (BUN) , red blood cell count (RBC) and its classification, white blood cell count (WBC) and its classification, platelet count (PLT), electrolyte ion concentration (K + , Na + , Cl-), prothrombin time (PT) were detected on the 91 d.RESULTS On the fasting group(♂) : TG, CHOlevels were decreased and TBIL, TP, ALB, WBC and Na+ levels were increased in serum(P <0.01);on the fasting group(♀) : TG, MCHC levels were decreased and TBIL, ALB and Na + levels were increased in serum (P < 0.01).CONCLUSION Fasting can influenceon the blood parameters of SPF SD rats.