Abstract: This study was to examine the effect of pH on physiochemical properties of trans- resveratrol nanoemulsions with pomegranate seed oil. First,trans- resveratrol self- nanoemulsifying drug delivery system with pomegranate seed oil( RES SNEDDS- PSO) was prepared using pomegranate seed oil as the oil phase. The physiochemical properties of nanoemulsions developed by RES SNEDDS- PSO with pH of 6.8,5.8 and 4.8 were investigated,respectively. The results showed that RES SNEDDS- PSO of various p H were converted into nanoemulsions with the diameter below 100 nm upon exposure to 10- fold water,and zeta potentials were-6.42,-2.10,and-0.661 mv,respectively. As the p H value declined,resveratrol solubility in nanoemulsions decreased,along with poorer physical stability and the slower release rate in vitro. RES SNEDDS- PSO of pH6.8 and 5.8diminished resveratrol degradation constant in water by one fold,while the degradation process of RES SNEDDSPSO of pH4.8 resembled to that of the control solution.Nanoemulsions formed by RES SNEDDS- PSO with various p H slightly accelerated the decomposition of resveratrol in gastric fluid,but significantly enhanced resveratrol stability in intestinal fluid.This study implied that the impact of pH on the stability of free resveratrol was different from that of RES SNEDDS- PSO.