Vitamin C is a six-carbon lactone that is synthesized from glucose in the liver of most mammalian species, but not by humans. Vitamin C is an electron donor and therefore a reducing agent. All known physiological and biochemical actions of vitamin C are due to its action as an electron donor and therefore it is good free radical scavenger. In humans, vitamin C acts as an electron donor for eight different enzymes. These vitamin C dependent enzymes required for collagen hydroxylation, synthesis of carnitine, norepinephrine, and peptide hormones and tyrosine metabolism. We have estimated the vitamin C levels in the plasma of the leukemic patients. The overall mean vitamin C levels in the leukemic patients were significantly low (0.25 ± 0.04) as compared to that of the normal control (0.90 ± 0.07). In respect to sex, the mean vitamin C levels in males (0.25 ± 0.04) were found to low than that in females (0.26 ± 0.04) however, we found significant difference only in patients with chronic leukemias. Whereas in respect to age, the mean vitamin C levels were found to elevated with increase in age (in < 10 years value was 0.23 ± 0.03, whereas in age >51 years value was 0.26 ± 0.04) indicating the extent of the free radicals might have stimulated the production of the antioxidant. We observed highly significant (p<0.001) vitamin C levels in all leukemic patients (AML, ALL, CML and CLL) with respect to age. Our results suggest that oxidative stress in leukemic patients causes the deficiency in antioxidant vitamin C, which arise as a result of enormous production of reactive oxygen species in the system.