Objective To evaluate the effect of low intensity He-Ne laser irradiation on the level of hydroxyproline in the Achilles tendons of rabbits after experimental tenotomy, and to determine the best irradiation cycle. Methods Twenty-two male New Zealand rabbits, aged 10-12 weeks, were randomly divided into control and experimental groups. The control group received no laser irradiation after tenotomy. The experimental animals were treated with a He-Ne laser (632.8 nm, 18.9 mW) daily for 14 days. The treated animals received 10 minutes, 20 minutes or 30 minutes of irradiation daily. At the 14th day or the 28th day after the operation, the rabbits were sacrificed and the level of hydroxyproline ( Hyp) in their Achilles tendons was measured. Results Hyp was significantly higher in all experimental animals than that in the controls. Hyp level in the 20 minutes group was significantly higher than in the 10 minutes group. Hyp level in the 20 minutes group at the 28th day were significantly higher than at the 14th day. Conclusions He-Ne laser irradiation facilitates the synthesis of collagen and enhances the healing of A-chilles tendons. The best irradiation time might be 20 minutes.