OBJECTIVE： To investigate the improvement effects of external application of water extract from Picrasma quassioides on allergic contact dermatitis （ACD） model mice， and to provide reference for its further development and utilization. METHODS： A total of 48 mice were randomly divided into blank control group （normal saline）， model group （normal saline）， hydrocortisone group （positive control， about 0.15 g/ear） and water extract from P. quassioides low-dose， medium-dose and high-dose groups （0.15， 0.3， 0.6 g/ear， calculated by extract）， with 8 mice in each group. The mice were given medicine on ear at 8 a.m. and 4 p.m. for 7 d continuously. Except for blank control group， other groups were given acetone-olive oil solution containing 0.5％ 2，4-dinitrofluorobenzene （DNFB） on the abdomen of mice to induce ACD model. After 7 d medication， modeling group was given acetone-olive oil of 0.25％ DNFB on left ear to induce dermatitis. 24 h later， the pathological changes of left ear tissue were observed by naked eye and skin lesion was scored. The thickness difference and weight difference of left and right ears in mice were measured. The serum contents of IL-6 and IgE were determined. The pathomorphology changes of ear tissue were observed by microscope after HE staining. RESULTS： Compared with blank control group， the skin lesion score of left ear was increased significantly in model group （P＜0.01）； the thickness difference and weight difference of left and right ears， serum contents of IgE and IL-6 were increased significantly （P＜0.01）. Pathological changes were observed in left tissue of mice by microscope， such as lymphocytic infiltration， intercellular edema， erythrocyte exudation. Compared with model group， skin lesion score of left ear in mice was decreased significantly in hydrocortisone group and water extract from P. quassioides high-dose group （P＜0.05 or P＜0.01）； the thickness difference and weight difference of left and right ears in mice were decreased significantly in all administration groups （P＜0.01）. The serum contents of IgE and IL-6 in mice were decreased significantly in hydrocortisone group， water extract from P. quassioides medium-dose and high-dose groups （P＜0.01）； the inflammatory lesions of left ear in mice were alleviated to varying degrees in different administration groups. CONCLUSIONS： External application of water extract from P. quassioides has a good improvement effect on ACD model mice.