In this study, the investigation of the effect of the blood withdrawal site on certain hematological values was aimed. For this purpose a total of 21 female Swiss albino mice were used. The mice were divided into three equal groups. Each group served for a different blood collection technique. Blood was withdrawn from the heart, the tail or from the retro-orbital plexus only for one time from each animal. The mean PCV value in blood gathered from retro-orbital plexus was higher than in blood collected from other two blood sampling sites (P<0.01). It was seen that the blood obtained from retro-orbital plexus had also higher mean leukocyte concentrations as a result of higher lymphocyte concentrations (both P<0.05). However, the percentage of eosinophils was highest in the tail blood, and the differences between blood samples obtained from tail and retro-orbital plexus were statistically significant (P<0.01). Similarly, the percentage of monocytes was highest in the hearth blood, and the differences with tail and retro-orbital plexus sites were statistically confirmed (P<0.05). It was concluded that blood composition may change depending on sampling site and the blood sampling site have to be taken into consideration when hematological and possibly serum biochemical values are evaluated.