Theileriosis is one of the most important diseases in tropical and subtropical regions and leads to annually economic losses such as the reduction of dairy products and casualties. Afghanistan is a country with dry climate. Despite the observed clinical form of Theileriosis, no comprehensive study has been conducted on this issue in Afghanistan.and in this study the species of Theileria, T.annulata is diagnosed by Semi-nested PCR method on the 18S rRNA gene. In the first study from 100 sample blood smears with an optical microscope 22 cases(%22) have piroplasm in the slide and result of PCR method from 100 EDTA blood sample being 74 cases (%74) were infected with Theileria. In the continuation of study using by Semi-nested PCR method It was all 74 cases positive and was Theileria and species of T.annulata. Among 78 ticks from, 43(56%) were male and 34(45%) were female with Hyalomma genus and Annatolicum species. Furthermore, among 319 collected ticks from body surface of cattle in this area, the number of male and female ticks was 163 (51%) and 156 (49%), respectively which included Hyalomma annatolicum (56.4%), Hyalomma excavatum (24.5%), Hyalomma asiaticum (1.8%), Hyalomma marginatum (1.54%), Hyalomma marginatum rufipes (0.9%), and 48 (15%) nymphs. According to the results, theileriosis is one of the most important diseases in Herat-Afghanistan and it seems that Hyalomma annatolicum is the main vector of Theileria parasite. Therefore, control programs should be performed in this area

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