The aim of this study was to investigate the effect of low–level laser therapy (LLLT) on pain relief and functional performance in patients with chronic knee osteoarthritis (OA). The results showed significant improvements in all assessment parameters in both groups compared to baseline. Active laser group showed significant differences in pain intensity at rest and movement, knee function, and ambulation duration when compared with the placebo group. Therefore, LLLT seemed to be an effective modality for short–term pain relief and function improvement in patients with chronic knee OA.