The transdermal absorption characteristics of ursolic acid in Hedyotis diffusa were investigated.The content of ursolic acid was determined by HPLC.Skin on the back of SD rats was utilized, Franz vertical diffusion cell was adopted to investigate transdermal performance of ursolic acid, and effect of azone, eucalyptus oil, synthetic borneol, water extract and alc. extract of H. diffusa on transdermal performance of ursolic acid was investigated.Ursolic acid was difficult to penetrate the skin, it must be added to certain transdermal absorption enhancer.Effect of enhancers on ursolic acid was in order of 5% ethanol extract>5% ethanol extract+2% borneol>5% water extract>2% azone+10% propylene glycol (PG)>2% eucalyptus oil>4% azone>3% eucalyptus oil>2% azone>1% azone.Azone and eucalyptus oil was good penetration enhancers for ursolic acid in H. diffusa, compound water extract and ethanol extract had a collaborative effect in promoting penetration.