The immune response of naturally infested cattle with Theileria annulata, and vaccinated with sheep pox virus vaccine was studied in compari­son with the immunity of vaccinated healthy ani­mals. Fourteen bulls were proved to be suscepti­ble to sheep pox virus vaccination via screening of their sera using serum neutralization test. Six of these animals were confirmed to be infested with theileriosis via examination of Giemsa stained blood smears and immunofluorescent in­vestigation of another blood films. Another six non^-infested animals beside the infested one with ^theileriosis were vaccinated at the same time with sheep pox virus vaccine and two healthy animals were kept as control. Heparinized blood samples were collected for evaluation of the cell mediated immune response using lymphocyte transforma­^tion assay and the sera were separated for evalua­^tion of the humoral immunity using serum neutralization, double antibody sandwich ELISA and dot immunoblot ELISA techniques. A challenge test using the virulent lumpy skin disease virus was carried out at 90 day post vaccination for evaluating the immune status of all animals. Re­sults revealed a significant decrease in lympho­cytic cells in animals infested with theileriosis and the level of lymphocytic cells varied accord­ing to the severity of infection. Also, the antibody litres and the challenge with virulent virus showed highly depressed of antibody levels in acute infested animals, partial suppression in chronic infested animals with theileriosis and pos­itive reaction to challenge in severely infected an­imals and controls. It could be concluded that the degree of theileriosis infestation in cattle should be considered during the vaccination campaign against lumpy skin disease to avoid the failure of vaccination.