Microemulsion(W/O) formulations were prepared using lecithin as a surfactant,isopropyl myristate as the oil phase,n propanol as cosurfactant,and water.Influence of water content on the phase behavior of the microemulsion system was evaluated via the conductivity method,visual examination,dynamic light scattering(DLS) and differential scanning calorimetry(DSC).The results showed that,the microemulsion became cloudy when its water content was up to 11.5% in the visual examination.The conductivity increased slowly before water content reached 3.85%,and then followed a rapid increase until 10.71% at which the conductivity turned to decrease.The microemulsion droplet sizes assessed by DLS decreased firstly,and then increased as water content increased,the turning point was at 5.66%.After reaching 10.71% of water content,droplet sizes increased dramatically by three orders of magnitude.DSC curves revealed that microemulsion did not show water freezing peak until water content came up to 3.85%.With the increase of water content,the water freezing peak shifted towards high temperature and peak area increased linearly.However,the freezing peak divided into two at water content of 11.5%.Based on the study results,it could be deduced that phase structure transition point from W/O to Bi-continuous were in water content from about 3.85% to 5.66%,while the system was turned to phase separation at 10.71%.