Abstract: Theileriosis is a bovine haemoprotozoal infection caused by Theileria species. It is a tick transmitted haemoparasite and the disease can develop as clinical or subclinical infections. This study was carried out in order to determine Theileria infection by Polymerase Chain Reaction in cattle and buffaloes in a National Livestock Development Board farm at Polonnaruwa, Sri Lanka. Forty-one blood samples were collected from the herd of diseased and non diseased cattle and buffaloes. Packed cell volume of each blood sample was analyzed using microcenrifugation which revealed that 85.7% (18/21) cattle and 20% (4/20) buffaloes had PCV values below the average. White Blood Cell count was calculated using haemocytometer method and 33.3% (7/21) cattle and 15% (3/20) buffaloes had WBC count above average value.