Abstract : Objective: To investigate the treatment effect of low intensity ultrasound combined with hydroquinone ointment on chloasma of SD rats in order to provide new ideas for clinical treatment of chloasma. Methods: Eighteen SD rats were randomly divided into control group, low intensity ultrasound combined with hydroquinone group, and hydroquinone group, with 6 rats in each group. The combined group was irradiated with ultrasound at the intensity of 0.32W/cm2 and frequency of 12min (42KHz); the hydroquinone group was evenly coated with hydroquinone to absorb after the hair removal; while the control group only expose the skin without any treatment. The changes of physiological indexes in SD rats were observed during the experiment. Plaque images were collected and the change trend was observed. Serum, liver, and skin were removed, and their SOD activity and MDA content were measured. Pathological sections of skin were made, and the changes of melanin granules were observed under optical microscope. Results: 1. There were no significant changes in physiological indexes before and after treatment among three groups of SD rats. 2.Plaque area in ultrasound combined with hydroquinone group reduced and became pale, while hydroquinone group did not show obvious changes. 3.After treatment, the activity of SOD was increased, while the content of MDA was decreased, with the changes being more obvious in the ultrasound combined with hydroquinone group. There was significant difference between the ultrasound combined with hydroquinone group and the hydroquinone group (P < 0.05). 4.Pathological observation showed that the number of black particles were reduced in the treatment groups, and the distribution of melanin granules was discrete in the combined group and linear in hydroquinone group. Conclusions: Low intensity ultrasound combined with hydroquinone is significantly superior to single hydroquinone in its bactericidal effect on SD rats with chloasma.