Background: Osteoarthritis (OA) is a cause of major disability, primarily affecting the knee joint with the hamstring muscle's shortening, tightening, and loss of muscle flexibility. Foam rollers improve flexibility, decrease pain intensity, and regulate muscle imbalance. Vibrating foam rollers (VFR) add the component of vibration therapy to traditional foam rollers. Purpose: to examine the effect of VFR on hamstring flexibility, pain intensity level, and functional disability of knee joint score in patients with chronic knee OA. Methods: 42 patients, ranging in age from 40 to 60 years, of both genders with mild to moderate unilateral chronic knee OA were randomly assigned into two groups of twenty-one patients each. Groups (A) and (B) received a conventional physical therapy program involving strengthening and stretching for muscles in the lower limbs for four weeks or three workouts per week. Group (B), additionally, received a VFR training program on the hamstring, three sessions per week for four weeks. The active knee extension test (AKE), visual analog scale (VAS), and Arabic version of the Western Ontario Osteoarthritis Index (ArWOMAC) were used to measure hamstring flexibility, pain intensity level, and knee joint functional disability, respectively. Results: There was a significant improvement (P<0.05) in hamstring flexibility, pain intensity level, and functional disability of the knee score joint in group (B) more than group (A). Conclusions: VFR improves hamstring flexibility, pain intensity level, and functional disability of the knee joint in patients with unilateral chronic knee OA.