Background: There is no a validated knowledge assessment tool to examine the relationship between patient knowledge regarding warfarin therapy and its safe and effective in Malaysia. Objective: To translate the Oral Anticoagulation Knowledge (OAK) Test into the Malay language (Bahasa Malaysia), and to examine the psychometric properties of the Malaysian version. Methods: In a prospective, parallel group study, 382 consecutive outpatients with atrial fibrillation prescribed warfarin treatment were identified between September 2011 and January 2013 at Hospital Pulau Pinang and Seberang Jaya Hospitals, Penang, Malaysia. To be included in the study, patients had to (1) have been diagnosed with Atrial Fibrillation at least one year before, (2) use Warfarin for more than 6 months medications, (3) be over 20 years of age, and (4) be able to communicate in the Malaysian language. Patients who had severe health problems or cognitive impairment and could not complete interviews were excluded. A standard translation procedure was used to develop the Malaysian version of the OAK from the original English version. Face-to-face interviews included administration of the translated 20-question test and a collection of socio-demographic data. Medical records were reviewed for INR levels and other clinical data. Reliability was tested for internal consistency using Cronbach’s alpha coefficient. Results: Only 215 were eligible and accepted to complete the questionnaires. The mean±SD of OAK scores was 47.6±17.6. Good internal consistency was found (Cronbach’s alpha = 0.767); the test-retest reliability value was 0.871 (p<0.001). For known group validity, a significant relationship between OAK categories and TTR (INR) categories (chi-square = 12.24; p <0.05) was found. Conclusion:The findings proved that the Malaysian version of the OAK is a reliable and valid measure of Warfarin knowledge that may be a useful tool for research and clinical practice. There is a need for improvement in patient education, including reinforcement of dietary guidelines for warfarin therapy as well as when it is appropriate to contact the clinic for questions.