Traditionally, the dyeing of natural dye from plant materials requires longer time and higher temperature to get good colour fastness. Thus, this study explored a suitable technique for more efficient natural dyeing using mordant to improve colour fastness of natural dyes. This study used ultrasound wave as a technique for dyeing the colourant from a selected plant (Ratanjot) to a selected fabric (cotton) and compared the conventional and ultrasonic dyeing methods in terms of its colour strength, CIE Lab values and color fastness to lightness, washing, rubbing and perspiration. The dye uptake percentage was found to be maximum by using ultrasonic dyeing technique as compared to conventional dyeing technique. Moreover, the cotton samples achieved by ultrasonic dyeing technique gave darker shade. Also, the fastness grades to light, washing, rubbing and perspiration also improved for the samples dyed with ultrasonic waves even at lower temperature. Therefore, the utilization of ultrasound wave for dyeing of natural dye found to be significantly improved in dye uptake and colour fastness with lower dyeing temperature compared to conventional dyeing technique.