Purpose: The aim of this study was to investigate gait differences via 3-D gait analysis system through osteoarthritis progression in patients with knee osteoarthritis and compare the results with healthy individuals.,Methods: According to Kellgren-Lawrence radiologic classification Grade I-II and III, a total of 45 patients (mean age: 54.02 +/- 6.58 years) with (aged between 41-65 years) bilateral knee osteoarthritis (female: 36, male: 9) and 14 (aged between 48-61 years) healthy individuals (mean age: 53.21 +/- 4.42 years; female: 12, male: 2) participated in the study. Gait analysis was performed via Vicon Gait Analysis System consisted of 6 infrared cameras and 2 force platforms.,Results: Knee flexion during swing phase and total knee flexion range of motion parameters were statistically lower in Grade II and III groups than the controls (p<0.008). Gait speed parameter was significantly slower in patients with Grade III group than Grade I and control groups. In addition, gait speed parameter was lower in Grade II than control groups (p<0.008). There was significant decrease in stride length parameter in Grade III group compared to Grade I and control groups (p<0.001).,Discussion: Distinctive kinematic changes were decrease in knee flexion angle during swing phase, gait speed and stride length parameters in patients with knee osteoarthritis. These variations were obvious accompanying with the severity of osteoarthritis. The possible reason for decrease in knee flexion angle during swing phase was thought decrease in gait speed.