Background. New studies in the management of knee osteoarthritis have focused on modern therapeutic methods stimulating cartilage healing process. In the present study, we evaluated the effects of 2 courses of leucocyte-rich PRP (LR-PRP) injections on patients' QOL and functions and also the relationship between the PRP concentration and mentioned variables. Material and Methods. Sixty-five patients were evaluated. For each participant, WOMAC and the native (Farsi) edition of the SF-36 questionnaire were filled. Two courses of LR-PRP injections with 4-week interval were used. After 6 months, SF-36 and WOMAC questionnaires were filled again for each patient. Results. 60 patients were included in the final analysis. The mean platelet concentrations and white blood cell in PRP was 5-fold increase and 220 per microliter, respectively. The mean total WOMAC revealed significant change (P = 0.001). In SF-36, the mean changes of 2 major physical and mental domains were meaningful (P = 0.001). Discussion. In our study, 2 injections of PRP, with 4-week interval, improved the pain, stiffness, and functional capacity. Improvements in QOL (both PCS and MCS) were meaningful after injections. These changes were more significant in physical domains. PRP injection may be an alternative therapy in selective patients resistant to current nonsurgical treatments of knee osteoarthritis.