Forty-eight patients with knee osteoarthritis were randomized to receive either 808nm (n=16) or 660nm (n=16) low-level laser therapy, or sham (n=16). The primary outcomes of this trial were knee extensor strength and knee flexion strength, one week after the 8-week intervention. Other outcomes of interest were the 30-second chair stand, 40-meter walking test, timed up and go (TUG) test, and the stair climbing test score. Knee extensor strength was significantly better in the 660 nm low-level laser therapy group when compared to the 808 nm group. The sham group was also significantly better for knee extensor strength compared to the 808 nm group. The sham group showed significantly better 40 m fast-paced walk test scores compared to the 808nm and 660 nm groups. No other differences were reported among groups for the other outcomes.