Most studies suggested that arthroscopic microfracture is effective method at only less than 40 years of age. Thus, the authors thought that "how can this indication regarding age be extended?," and tried to find a way to use this technique effectively over 40 years of age. The aim of this study was the first to report the results regarding the PRP as an adjunct for arthroscopic microfracture in the early osteoarthritic (OA) knee with cartilage lesion over 40 years of age. 49 patients who underwent arthroscopic microfracture for cartilage lesion sized less than 4 cm(2) with early OA, aged 40-50 years, were enrolled and randomly divided into 2 groups: a control group with only arthroscopic microfracture (25 patients) and a study group with arthroscopic microfracture and PRP (24 patients). The patients were prospectively evaluated with VAS, IKDC score at preoperative and postoperative 1, 6, 12, and 24 months. And we perform second arthroscopies in 10 patients of each group to identify the extent of cartilage restoration at 4-6 months postoperatively. There were significant improvements in clinical results between preoperative evaluation and postoperative 2 years in both groups (p = 0.017). In the postoperative 2 years, clinical results showed significantly better in the study group than in the control group (p = 0.012). In post-arthroscopic finding, hardness and elasticity degree was better in the study group. The PRP injection with arthroscopic microfracture would be improved the results in early osteoarthritic knee with cartilage lesion in 40-50 years old, and the indication of this technique could be extended to 50 years.