The purpose of the study was to produce soy protein isolate(SPI) micro emulsion droplet by ultrasonication and microfluidization Techniques. The changes of SPI emulsion temperature, average droplet diameter and size distribution were observed. The distribution curve of SPI droplet processed by ultrasonication has two peaks and that of SPI droplet processed by microfluidization has single peak. The results indicate that the SPI emulsion processed by high pressure is more homogeneous. The capability of reducing size by ultrasonic process (1 200 W) is very limited, and the SPI emulsion tends to agglomerate after a long time of ultrasonic process. Microfluidization (microseconds, 35 MPa) can provide high energy and has the rather better affection for micronizing the treated SPI emulsion (hundred micrometers), and the mean droplet diameter D_\[3,2\] and D_\[4,3\] are exponentially shortened.