This study was carried out to determine the effect of vitamin E on some hematological parameters in subclinical mastitic dairy cows. Forty cows were assigned to two groups by California Mastitis Test (CMT) and somatic cell count (SCC). Vitamin E (2.000 IU) was injected to cows of mastitic group by intramuscular route overnight for twenty days. The blood samples from healthy, pre-treatment and post-treatment mastitic group cows; total leukocyte, erythrocyte counts, hemoglobin and haematocrit values, mean corpuscular hemoglobin of erythrocyte, mean corpuscular hemoglobin concentration of erythrocyte and mean corpuscular volume of erythrocyte parameters and percentages of neutrophils, eosinophil, basophil, lymphocyte and monocyte were analysed. Differences in hemoglobin (P<0.05), haematocrit (P<0.01), eosinophil (P<0.05) and lymphocyte (P<0.01) values between healthy and mastitic pre-treatment groups were significantly changed while differences in total leukocyte, erythrocyte counts values, mean corpuscular hemoglobin of erythrocyte, mean corpuscular hemoglobin concentration of erythrocyte and mean corpuscular volume of erythrocyte values, neutrophyl, basophil and monocyte values (P>0.05) were not significant. Pre-treatment and post-treatment mastitic groups in haematocrit (P<0.05), eosinophil (P<0.001), lymphocyte (P<0.05) and monocyte values (P<0.05) were found as stastistically significant whereas differences in total leukocyte, erythrocyte and hemoglobin counts values, mean corpuscular hemoglobin of erythrocyte, mean corpuscular hemoglobin concentration of erythrocyte and mean copuscular volume of erythrocyte values, neutrophyl and basophil values (P>0.05) were not significant.