Cobalt (Co) is an essential trace element and its accumulation affects the concentrations of other elements also. Co(II) is shown to compete with iron (Fe) for the transferrin receptor and to form a stable complex with haemoglobin thus affecting haematopoiesis. There are lack of data regarding the effect of chronic exposure to Co compounds on Fe content in spleen and liver of mice. The study deals with the effect of long-term treatment with cobalt-EDTA (Co-EDTA) on iron content in the spleen and liver of immature mice. Pregnant ICR mice were subjected to chronic treatment with daily dose of 75 mg/kg Co-EDTA which continued until day 25pnd of the newborn pups. Results show accumulation of Co(II) and altered Fe content in the spleen and liver of treated mice compared to age-matched controls with significantly increased Fe concentration in the livers of treated mice. The changes could explain impaired haematopoiesis and immune responses of exposed to Co(II) immature mice