OBJECTIVE： To investigate the property， skin irritation and in vitro transdermal absorption of Diclofenac sodium microemulsion （DS-ME）， and to explore the feasibility of local external use of it. METHODS： The content of DS in DS-ME was determined by ultraviolet spectrophotometry. The distribution of particle size was determined by laser particle size analyzer. The effects of DS-ME and blank micro-emulsion on normal skin of single administration， normal skin of multiple administration and damaged skin of single administration were investigated by rabbit skin irritation test. The transdermal parameters of DS-ME and commercially available DS gel through isolated skin of mice were compared by Franz diffusion cell. RESULTS： The prepared DS-ME was O/W microemulsion with particle size of （30.140±9.020） nm. Compared with blank ME， DS-ME had no significant difference in rabbit skin irritation score. Steady permeation rates of DS-ME and commercially available DS gel were 34.16 and 18.62 μg/（cm2·h）， respectively； the permeation coefficient of them were 1.029 and 0.561 cm/h； the delay time were 0.124 2 and 0.367 2 h. CONCLUSIONS： The particle size of DS-ME is small and not irritant to skin， and can improve  transdermal absorption rate of DS.