The present study aimed to determine the prevalence of ovine theileriosis (OT) in sheep in Mosul city, Iraq using microscopic examination (ME) of the blood smears stained with MGG-Quick stain and conventional polymerase chain reaction technique (c-PCR) to compare between c-PCR technique and ME as techniques for the diagnosis of disease, and to investigate the pattern and type of infections based on multiplex polymerase chain reaction technique (m-PCR). From October 2021 to May 2022, one-handed eighty-five Blood samples were drawn randomly from sheep in various regions of Mosul city. The overall prevalence of OT was 42% (22.7 out of 185) and 52.4% (97 out of 185) using microscopic examination and c-PCR technique, respectively. A slight agreement was observed between ME of blood smears and c-PCR technique according to Kappa value 0.190, with low sensitivity, specificity, and accuracy of ME method was 30%, 88.6%, 58.4%, respectively, compared with c-PCR technique. The prevalence of mixed infection 22.7% and single infection with T. lestoquardi 20% were significantly higher (P<0.05) than single infection with T. ovis 9.7%. This study concludes that OT is widespread in Mosul city, Iraq, and the c-PCR technique is more reliable and suitable for detecting Theileria infection in sheep than the ME method.