Theileriosis is a common protozoan disease in cattle that affects a large population of cattle in the region annually. The present study was conducted in order to investigate of serum iron, phosphorous, cobalt levels of infected cows. 41 infected cows were identified based on laboratory and clinical signs at the large livestock clinic of a Tabriz Islamic Azad university, veterinary college. The blood sample was obtained from any cow’s jugular vein followed by serum isolation. Simultaneously, 30 cattle of identical situation about age, feeding and management (with those 40 cattle) were sampled. Serum cobalt levels were measured using the atomic absorption method and the levels of phosphorous and iron were measured by means of Pars Azmoon biochemical kits. The mean level of iron in affected cattle was lower meaningfully compared with healthy cattle (p= 0.000). The mean rate of serum cobalt in affected cattle was meaningfully higher compared with healthy cattle (p= 0.001), but the increase of serum phosphorus was not significant in affected cattle (p = 0.632). There was not any relationship between age and iron, phosphorous, cobalt levels of affected cattle. Based on the percentage of affected animals’ blood hematocrit, serum level of phosphorus and cobalt didn’t change significantly but the serum iron decreased with the decrease of hematocrit percentage and the mean difference of serum iron in affected cattle was significant based on the percentage of hematocrit (p=0.030). We concluded that in Theileriosic cattle the serum levels of iron, phosphorous, cobalt were high. Regarding to the occurrence of anaemia in affected cattle and the role of iron in hematogenesis and the immune system as well as the main role of the phosphorous and cobalt, the use of complements containing the three elements orally or as an injection form of affected cattle is recommended.