The Anterior Cruciate Ligament (ACL) rupture reduces knee stability. In old patients with ACL rupture, surgery is not recommended due to the person's low level of activity and knee osteoarthritis. Platelet-rich plasma (PRP) is a good treatment option in inflammatory cases in orthopedics. Hence, the aim of this study was to assess and comparison of the effect of PRP and arthroscopic surgery on anterior cruciate ligament rupture. This is a clinical trial that was performed in 2020-2021 in Tehran. 100 patients were randomly divided into two groups. The first group of patients underwent ACL tendon repair surgery by arthroscopy and tendon graft. The second group were treated by PRP injection. Both groups of patients were visited from 3 months to 14 months after surgery or PRP treatments. The pain was assessed by Visual Analogue Scale (VAS), we also used Knee Score by the Oxford Score Knee Outcome Scale (OKS) to assess patient’s functions. The mean VAS score was 3.05 ± 2.47 in patients in surgery group and mean VAS score was 4.39± 2.66 in patients in the PRP group (p = 0.03). These data showed significant improvements in VAS score in both groups with higher improvements in surgical group. After procedures, the ROM was 120.33 ± 19.60º in surgery group and 109.31 ± 17.22º in PRP group (p = 0.03). Patients in both groups had significantly decreased pain severity after 14 months, but the patients in the surgical treatment group had significantly lower pain and higher ROM compared to PRP group.