[Purpose] The purpose of this study was to examine the effect of closed kinetic chain exercises performed by an unstable exercise group (UEG) and a stable exercise group (SEG) on the knee joint, proprioception, and functional scores of patients who underwent anterior cruciate ligament (ACL) reconstruction. [Subjects] Twenty-eight patients participated in this study. The exclusion criteria were fracture or neurological disease. [Methods] The subjects were randomly assigned to one of two groups, each with 14 people. Each group took part in a 60-minute exercise program, three times a week for six weeks. [Results] The results of the clinical evaluation at 45°proprioception showed statistically significant differences between the two groups. The results of the clinical evaluation at 15°proprioception showed no statistically significant differences between the two groups. [Conclusion] The proprioception and functional scores of the patients in the UEG who underwent ACL reconstruction were superior to those in the SEG group.