The aim of this study was to investigate changes in hematological values after feeding diet mixed with oil pressed from seeds of Nigella sativa in sheep. The results indicated that there was no effect on the total Red Blood Cells (RBCs) count due to treatment when compared to the control group, but the treated group showed significant (P≤0.05) increase in the total RBCs count after six weeks compared to the transient decrease at week two. Hemoglobin concentration showed similar pattern to what was observed in the RBC count in both the treated and control groups. Packed Cells Volume (PCV), Mean Carpuscular Volume (MCV), Mean Carpuscular Hemoglobin (MCH) and Mean Carpuscular Hemoglobin Concentration (MCHC) weren't affected by feeding N. sativa oil to sheep throughout the experiment. However, there were significantly (p≤ 0.05) lower values in total mean of White Blood Cells (WBCs), lymphocytes and granulocytes of the treated group compared to the control. The levels of White Blood Cells in the treated group were not time dependent. The Monocytes total mean was similar in both groups but the cells were significantly (P≤0.05) lower in the N. sativa oil treated group compared to the control at week four. The hematological changes could be due to N. sativa volatile oils incorporated Original Research Article