The oxygen capacity of the blood of 64 albino Rattus norvegicus (Sherman strain) was determined by the microgasometric syringe method. Data were obtained showing the relationship of blood oxygen capacity to weight and sex of the animals. It was found that blood oxygen capacity in volumes per cent increased as the weight of the rats increased. Statistically, there was no difference in the blood values in either male or female rats as analyzed in different weight groups and ranges. Also, the oxygen capacity of the blood per unit of body weight decreased as the weight of the rats increased.