Microemulsions (O/W,W/O and B.C.) formed in Tween80/ethanol/ethyl butyrate/water system were identified by phase diagram determination and conductivity measurement at 25℃.Influences of temperature,salinity as well as pH on the area of microemulsion region were investigated.Moreover comparative studies were made,by means of dynamic light scattering,viscosity and UV measurements,on (1) the difference of viscosity and particle size between β-carotene solubilized and empty microemulsions; (2) the effects of sunlight and temperature on the stability of β-carotene both in microemulsion and in ethyl butyrate solution.It is shown that the area of microemulsion region decreases slightly with increase of temperature and decrease of pH value.