Abstract: In cross-sectional survey conducted in River Nile State, Northern Sudan, 1905 blood smears from sheep were examined for the presence of Theileria piroplasms. Out of 800 samples from resident sheep 177 (22.1%) were found infected, while in 1105 samples from slaughterhouse 197 (17.8) were infected. Thirteen out of 210(6.2%) Hyalomma anatolicum anatolicum ticks were found infected with Theileria sporoblasts. The number of infected acini per salivary glands was significantly higher (P<0.01) in female ticks (1.56) than in male ticks (1.0). Combining infection rate in ticks with infection prevalence studies lead to improved understanding of the epidemiology of malignant ovine theileriosis in the River Nile State, Northern Sudan. The results also indicated year-round transmission of the parasite in the study area.