Introduction: Haemophilia A is an X - linked recessive bleeding disorder caused by dysfunctional or decient production of coagulation Factor VIII. Development of antibodies against the exogenous Factor VIII is the major cause for refractoriness in the treatment of Haemophilia A. These antibodies are known as inhibitors. Aim: Estimation of prevalence of Factor VIII inhibitors in Haemophilia A patients by inhibitor screening assay. Determination of Factor VIII activity by Factor VIII assay in these patients and Quantify Factor VIII inhibitors by Bethesda assay. Methods: This study was carried out between January 2019 and December 2020. We studied 59 patients who were on “On-demand Plasmaderived factor VIII therapy” at the Haemophilia Treatment Centre- Royapetttah Government General Hospital, Chennai. Factor VIII level estimation, inhibitor screening assay and quantitative Bethesda assay were done at the Department of Transfusion Medicine, The Tamil Nadu Dr M.G.R Medical University. Results: Out of 59 patients screened, 31, 26 and 2 were diagnosed as severe, moderate and mild Haemophilia A respectively. Five of them developed inhibitors, two were newly diagnosed and three were known cases. The prevalence was 8.5%. All patients with inhibitors had <1% residual Factor VIII activity. Three had positive family history. By Bethesda Assay, two had high and three showed low titre Factor VIII inhibitors. Conclusion: The prevalence of Factor VIII inhibitor in our study is similar to other studies. We observed positive family history in majority of these patients. Since prophylactic factor VIII therapy delays inhibitor development, further study is recommended