Osteoarthritis (OA) is a degenerative disorder resulting from loss of joint cartilage and underlying bone and causes pain and loss of function. The treatment of knee OA is still a challenge because of the poor self-regeneration capacity of cartilage. The nonsurgical interventions include control of the aggravating factor (such as weight control and the use of walking aids), symptomatic treatment (such as acetaminophen or nonsteroidal anti-inflammatory drugs), prolotherapy, and viscosupplementation. However, the combination of platelet-rich plasma (PRP) and hyaluronic acid (HA) has not been widely used because of lack of clinical evidence and several limitations in patients with severe knee OA. Three patients who suffered from knee pain and poor walking endurance were diagnosed with advanced knee OA. They underwent PRP treatment in association with intra-articular HA injection and showed pain relief and functional improvement. The follow-up standard weight-bearing X-ray images of knees also confirmed the improvement and indicated the possibility of regeneration of the articular cartilage. These cases provide clinical and radiographic evidence for a new therapy for advanced knee OA. This treatment strategy of PRP in association with HA injection can offer a chance to treat severe knee OA, rather than immediate surgery, or a chance for those who cannot undergo surgery. It can also postpone the need of arthroplasty and can significantly improve the daily activity function.