ABSTRACT Neutropenia is one of the adverse effects caused by the administration of chemotherapy drugs. The present study aimed at investigating the effect of vitamin C supplementation in a model of immunosuppression induced by cyclophosphamide in mice. Vitamin C supplementation (50 mg/kg/day) administered intraperitoneally (i.p.) for 7 consecutive days in adult Swiss albino female. Mice were divided into four groups (n= 8/group): 1. Control (only distilled water i.p.), 2. Cyclophosphamide group (cyclophosphamide i.p. 150 and 100 mg/kg on days 1 and 4, respectively and distilled water daily), 3. Vitamin C group (Vitamin C 50 mg/kg i.p. and distilled water daily), and 4. Cyclophosphamide and Vitamin C group (cyclophosphamide i.p. 150 and 100 mg/kg on days 1 and 4, respectively and vitamin C 50 mg/kg i.p. daily). Vitamin C did not interfere in leukocytes count, but when co-administered with cyclophosphamide, significant interaction was observed, intensifying the neutropenia caused by cyclophosphamide. Vitamin C did not influence body weight during treatment, but groups receiving cyclophosphamide had a significant weight loss from the third day of treatment until the end of experiment compared to the control group. Vitamin C supplementation intensified neutropenia induced by cyclophosphamide and did not prevent weight loss induced by cyclophosphamide in mice.