The objective of our study was to investigate the outcome of an active non-operative treatment of the acute isolated posterior cruciate ligament (PCL) injury using cylinder cast immobilization and brace with tibial supporter. This study included 17 acute and isolated PCL injuries with two years or more of follow-up for each patient. We applied a cylinder cast immobilization with tibial supporter with full extension of the knee for 6 weeks, and then another 6 weeks of PCL brace with tibial supporter and posterior elastic rubber band to prevent posterior sagging of the proximal tibia. There was improved anteroposterior stability with some residual laxity and improved clinical results at the last follow-up. The conservative treatment utilizing cylinder cast immobilization and brace may be one of the recommendable treatment methods in an isolated and acute PCL injury.