Background: A peroneus longus tendon autograft is used in many orthopaedic procedures and it is biomechanically comparable to a hamstring tendon autograft. Despite its potential, there are few studies that have evaluated the use of the peroneus longus tendon in ACL reconstruction. The purpose of this study is to evaluate the functional outcome and donor site morbidity ofsingle bundle ACL reconstruction using peroneus tendon graft. This study considers the usage of peroneus longus tendon autograft as a graft of choice in ACL reconstruction. Material and methods: This prospective study was done across two different tertiary hospitals from April 2017 to June 2020. A total of 100 patients gave informed consent to be included in this study and underwent single bundle ACL reconstruction using peroneous tendon graft. The functional scores (International Knee Documentation Committee (IKDC), Modified Cincinnati, Tegner-Lysholm score) were recorded before the surgery and after the surgery. Results: Out of 100, 80 patients were male and 20 patients were female. Mean age of the patients was 27.25 ± 9.11 with range from 19 to 46 years old. Injury mechanism of the patients was motorcycle accident 7 patients, sport injury 75 patients, and others injury 18 patients. Diameter of the peroneus longus graft was measured and recorded intraoperative, and the result peroneus longus graft mean diameter was 8.55 ± 0.73 mm. The mean of thigh circumference at 10 cm from upper pole of patella bone was 44.77 ± 2.87 at injury site and 45.95 ± 2.97 at contralateral site. The mean of thigh circumference at 20 cm from upper pole of patella bone was 52.77 ± 3.73 at injury site and 53.83 ± 3.55 at contralateral site. Result of mean IKDC score pre-operative was 55.77 ± 15.11 and post-operative was 96.12 ± 3.52. Mean Modified Cincinnati score pre-operative was 66.12 ± 17.32 and post-operative was 94.36 ± 7.21. Mean Tegner-Lysholm score pre-operative was 68.45 ± 15.65 and post-operative was 90.44 ± 8.56. Conclusion: ACL reconstruction with peroneus longus autograft has excellent functional score in IKDC, Modified Cincinnati, Tegner-Lysholm score at 1-years follow up with the advantages of greater graft diameter, less thigh hypotrophy, good serial hop test result, and excellent ankle function based on AOFAS and FADI score.