BACKGROUND: Ovine anaplasmosis and theileriosis are important tick-borne diseases of sheep and goats which are distributed in the tropical and subtropical areas of the world. OBJECTIVES: This study was performed to assess hematological status in sheep naturally infected with Anaplasma and Theileria spp. to clarify the pathogenic aspects of various species involved in ovine anaplasmosis and theileriosis in Ahvaz region. METHODS: 109 sheep were sampled, and blood parasite infections were diagnosed by microscopic examination and PCR. The blood samples were also subjected to hematologic assessment. RESULTS: PCR analysis revealed A. ovis infection in 86.2% of sheep, while mixed infections with A. marginale were also detected in 53.2% of them. However, Anaplasma inclusion bodies were only observed in 32.1% of the tested animals. T. ovis were found in 88% of the inspected sheep by PCR, and 67.8% of them were detected microscopically, as well. Hematologic assessment showed that mean RBC, PCV, Hb, and MCHC were significantly lower, whereas MCV and RDW were higher in the animals with mixed infections of Anaplasma with parasitemia and Theileria, compared to the uninfected sheep and groups with single infection or without parasitemia. CONCLUSIONS: In brief, it seems that Anaplasma can be activated and induce its pathogenesis in the presence of other infective agents in the carrier or asympthomatic animals. It can also be concluded that mixed infections of Anaplasma with parasitemia and Theileria may induce a regenerative anemia which is most likely attributable to a combined effect of the two.