The effect of an ultrasound field on the rheological properties and thermal stability of rapeseed oil (RO) in the presence of monoethanolamine (MEA) and the dispersing properties of the RO-MEA system were investigated. The extremal character of the change in the dispersing effect of RO with an increase in the concentration of MEA was established. Ultrasound vibrations cause mechanochemical transformations that decrease the thermal stability at high temperatures.