The objective of the present study were to evaluate hemogram, acute phaseresponse, acid base balance and blood gas analysis in newborn calves infected withTheileria annulata . The study was conducted on 55 local newborn calves (male andfemale), 1-9 days old. The study was carried out in Mosul , Iraq. Forty five newborncalves were infected with Theileria annulata. and Ten clinically normal calves servedas controls. Diseased calves showed sings of fever ,unilateral or bilateral visibleswelling of superficial lymph nodes. pronounced upward bulging of temporal fossa,outward bulge of conjunctivae with exophthalmos, paleness and/or icteric mucusmembranes with petechial hemorrhages on the conjunctiva, lacrimation, dyspnea anddepression. There was a significant reduction in the mean values of erythrocytescount, Hb and PCV,in diseased newborn calves infected with Theileria annulata andanemia was of Macrocytic hypochromic type. The percentage of hemoparasitism(parasitemia) ranged between (3-18%) with a mean of (11.88%). Results alsoindicated significant increase in total leukocytes count as results of significantincrease lymphocytes. Diagnosis of Theileriosis were confirmed by microscopicalexamination of Giemsa stained lymph node aspirate and peripheral blood smears.Results were also showed significant decrease in blood pH,Pco2,Bicarbonate, Baseaccess and Oxygen saturation percent(So2) ,However significant increase in Aniongab was found and Titritional metabolic acidosis were indicated. Moreover resultsshow significant decrease in haptoglobin and fibrinogen in diseased newborns calvesthan in controls.It have been concluded that Theileria annulata infection in newborncalves resulting in serious effects and health deterioration, leading to substantialsignificant economic losses