Objective: The purpose of this study was to investigate the effects and minimum effective dose of laser acupuncture in knee osteoarthritis (KOA), and to determine if it is superior to placebo treatment (sham) in the evaluation of clinical-functional outcome and quality of life. Methods: In this randomized, placebo-controlled study, patients with grade 2 and 3 primary KOA were selected. Group I (n = 27) received 904-nm low-level laser irradiation with 10 mW/cm(2) power density, 4 mW output power, 0.4 cm(2) spot size, 0.48 J dose per session, and 120-sec treatment time on the medial side of the knee to the acupuncture point Sp9. Group II (n = 25) received placebo-laser therapy at the same place on the same point. Patients in both of the groups had treatment 5 days per week (total duration of therapy was 10 days) and 20 min per day. The study was comprised of a 2-week (10-session) intervention. Participants were evaluated before treatment (baseline), after treatment (2nd week), and at the 12th week. In this double-blind study, a blind examiner carried out all outcome assessments. The main outcome measures were as follows: pain on movement (pVAS), 50-foot walking time (50 foot w), knee circumference (KC), medial tenderness score (MTS), Western Ontario and McMaster Universities osteoarthritis index (WOMAC), and Nottingham Health Profile (NHP). Results: Statistically significant improvement was observed in PVAS, 50 foot w, and KC in group I. In Group H, statistically significant improvement was observed in PVAS, 50 foot w, and WOMAC. When groups were compared with each other, the improvement observed in KC was superior in Group I at the 2nd week (p = 0.005). Conclusion: Laser acupuncture was found to be effective only in reducing periarticular swelling when compared with placebo laser.