The major agent of equine piroplasmosis (EP), Theileria equi, contributes to significant losses in the equine industry. This study was designed to evaluate T. equi infection among horses from West Azerbaijan by microscopy and molecular approaches. One hundred and twenty six blood samples were collected from the jugular vein and placed in sterile tubes containing EDTA; these tubes were either used immediately for blood smears or stored at –20°C for later examination by PCR. T. equi was detected in 3.2% and 27.7% of the animals examined using light microscopy and PCR methods, respectively. The prevalence of T. equi was higher in older animals (30.4%) than young equines (24.6%). Also, the females (31%) demonstrated higher T. equi infection rates than the males (23.6%). Additionally, while 12 horses housed with other animals were positive for T. equi, 23 not housed with other animals were found to be infected. No significant difference was found between infection rate and associated risk factors (age, sex, and housing with other animals). The results confirm a relatively high prevalence of T. equi in horses in the study area and also suggest that Equine Merozoite Antigen (EMA)-1 could be a strong candidate to develop diagnostic methods for T. equi infection. Due to the importance of EP in the equine industry, and the ability of animals to be lifelong carriers of T. equi, accurate and early diagnosis of the disease, based on specific antigens, is critical. Diagnosis would provide basic information about its epidemiology, distribution and prevalence, especially in apparently healthy animals, and effective control and vaccine measures.