Aim: Kefir is a probiotic/prebiotic drink with an exotic flavor, which has been traditionally produced with fermented milk and kefir grains containing a mixture of bacteria and yeast. Cyclophosphamide (CPx), are generally limited due to numerous unwanted and severe acute toxic side-effects. For this purpose, the cell-protective effects of kefir, a natural probiotic known for its antitumor and antioxidant properties, on CPx-induced hemotoxicity and myelotoxicity were investigated. 
 Methods: Group 1 using as control. Group 2 were administered a single dose of 150mg/kg CPx while Group 3 and 5 were given 5 and 10mg/kg kefir. Group 4 and 6 were given 5 and 10mg/kg kefir+150mg/kg CPx. While kefir was administered to the rats for 12 days, CPx was administered as single-dose on the 12th day. 
 Results: The DPPH results show that kefir possesses high antioxidant activity. It was observed that the leukocytes, thrombocytes, erythrocytes, hemoglobin, hematocrit and bone marrow nucleated cell levels decreased in the group that was administered only CPx, and increased relatively in the groups that were administered CPx+kefir, drawing close to the control. 
 Conclusion: The results of the present study also showed that kefir demonstrated antioxidant and cytoprotective activity, protecting blood and bone marrow cells against CPx-induced damage.