Abstract：Objective：the effects of low intensity laser irradiation on the chondrocyte proliferation and its mechanism were studied.　Methods: the chondrocytes isolated from the cartilage sample of 3-week-old New Zealand white rabbits were cultured with 10 % newborn calf serum (NCS), irradiated by 650nm semiconductor laser irradiation (SLI) at 2.96 mW/cm2 for 1 min, 3 min, 5 min, 7 min, 10 min and 20 min per day for 6 days, and then incubated till the 13th day at 2.5 % NCS. The type II collagen synthesis was assessed by a hydroxyproline (Hpr) content measurement on the 2nd, 4th, 6th, 8th, 10th and 12th day after the first SLI irradiation, respectively. The proliferation on the 13th day was assessed by a XTT assay. Results There is significant photobiomodulation on the proliferation of the chondrocytes cultured at 2.5% NCS. (1) The chondrocyte proliferation was significantly (P<0.01) promoted for the groups irradiated by SLI for 3, 5, 7 and 10 min, respectively, on the 13rd day；(2) The type II collagen synthesis increased steadily with days in the group irradiated by SLI for 5 min. Conclusions: the proliferation of the chondrocyte cultured at 2.5 % NCS might be promoted by SLI, which might be mediated by collagen synthesis.