Background: Osteoarthritis of the knee, the disease of knee joint dysfunction and pain caused by joint degeneration, it is the commonest joint disease. In most cases of joint degeneration there is no clear identifiable cause, but increasing age, excessive joint loading, and joint abnormalities and trauma increase the risk of OA. It has significant effects on human health and quality of life (QoL). Objective: This study was carried out aimed to determine the prevalence and determinant factors of osteoarthritis of the knee among elderly population in Arar, KSA. Methods: The present cross sectional community based study was conducted in Arar city, the capital of Northern Borders Governorate on 238 elderly people of age 60 years and more. Data was collected through personal interviews with the sampled population and filling a predesigned questionnaire. It included questions regarding the already previously diagnosed osteoarthritis of the knee joint and its determinants. Results: the mean age (± SD) was 70.4 (±9.3) years, male to female ratio was 48.3 to 51.7. The overall prevalence rate of osteoarthritis of the knee joint was 24.5%.Osteoarthritis was almost equal in females and males (26.8% and 26.1%, respectively), it was insignificantly associated with increasing age, female sex, hypertension and diabetes (P>0.05), while significantly associated with the BMI. Conclusion: Osteoarthritis of the knee joint is common among elderly population in Arar, KSA. It was almost equal in females and males.