Biodiesel may be produced by vegetable oil transesterification, followed by purification steps of product sedimentation and water washing. The occurrence of stable emulsions during the purification steps in the biodiesel production process from castor oil is a severe problem that precludes its use as an industrial raw material. The stability behavior of emulsions formed by castor oil biodiesel-water with 10, 20, and 30% (w/w) water content was studied using laser light profiling. Emulsion stability showed a decrease for emulsions with 10-20% water, but emulsions with 30% water showed a very high stability. Demulsification of water in biodiesel emulsions using microwave irradiation was also investigated as a function of the water content, separation temperature, and stirring speed. Analysis of the separation efficiency results showed that all of the variables were statistically significant but that water content was the most important factor. A comparison of microwave irradiation to gravitational sedimentation showed that a higher separation efficiency is obtained for emulsions submitted to the microwave irradiation.