The prevalence of bovine theileriosis and anaplasmosis were studied in dairy cattle in Mashhad area, Khorasan province in Iran from 2001 to 2002. A total of 160 dairy cattle from 78 farms were clinically examined and investigated for the presence of Theileria spp and Anaplasma spp in appropriate blood smears. The study revealed that the infection rate for Theileria annulata and Anaplasma marginale were 32(20%) and 15(9.38%), respectively. Double (mixed) infections occurred in 9 (5.62%) cattle. The acute theileriosis were observed in 23 (14.37%) of dairy cattle. The difference in Theileria annulata infection rates in male and female and different age groups of dairy cattle were statistically significant. Seasonally, prevalence of Theileria annulata infection in dairy cattle was highest level in summer (45%), while lowest level was observed in winter (2.5%). In addition, the prevalence of Anaplasma marginale infection in related to sex, age and season factors were not statistically significant. Keywords: theileriosis , anaplasmosis, dairy cattle, Iran

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