The erythrocytic-stage surface protein equi merozoite antigen 1 (EMA-1) of Theileria equi is a major candidate for the development of a diagnostic antigen for equine piroplasmosis. In this study, BALB/c mice were immunized with purified recombinant EMA-1 to prepare monoclonal antibody (mAb) against T. equi EMA-1, and 1 mAb 5H2 was obtained that showed good reaction with infected red blood cells (RBC) in the indirect immunofluorescence assay (IFA). To develop a rapid serological detection method for T. equi infection in Xinjiang Uygur Autonomous Region, China, recombinant EMA-1 originating from the local T. equi strain and the mAb to EMA-1 were employed to develop an immunochromatographic test (ICT) to detect antibodies to T. equi in horse sera. The ICT showed high sensitivity and specificity and no cross-reaction with Babesia caballi. Ninety-two horse serum samples collected from Ili, Xinjiang, were tested by ICT and compared with the detection results of a commercial ELISA kit. The results showed that 56 of 92 (61%) serum samples were seropositive according to the ICT assay, and 50 (54%) samples were seropositive according to the ELISA kit. The ICT had a high coincidence (91.3%) but was more sensitive than the reference ELISA kit. To confirm whether the horses were infected by T. equi, 30 blood DNA samples from 92 horses were examined by PCR. The results showed that 14 of 30 (47%) horses were confirmed to be infected with T. equi by PCR, while 16 of 30 (53%) horses were seropositive by ICT. All PCR-positive horses were ICT-positive. The findings indicate that T. equi is endemic in Ili, Xinjiang, and that the ICT is reliable as a serological diagnosis method. The ICT developed in this study could be an efficient diagnostic tool to detect T. equi infection in horses in the Xinjiang area.