Objective To study the effect of different gender,age and microbiological background on normal values of blood in Wistar rats. Methods Coulter JT was used for measuring the normal values of blood. Results There were very significant differences between aged male and female SPF Wistar rats in the values of RBC, Hgb, MCV, MCH, PLT, RDW ( P <0 01),and significant differences in the values of WBC,Neut ( P <0 05).By comparing conventional Wistar rats with SPF Wistar rats, the WBC,Neut,Lym,RBC,PDW,MPV had very significant differences( P <0 01),and Hgb,HCT,MCV,PLT had significant differences( P <0 05).For differences between young and aged Wistar rats, Neut,Mono,Hgb,MCH,PDW,MPV were very significant( P <0 01), and WBC,PLT were significant( P <0 05).Conclusion Different gender,age and gender, microbiological background of Wistar rats can affect their normal values of blood.