In this research dyeing behavior of organic cotton woven fabric using ultrasonic technique and conventional dyeing method has been compared. The fabric samples were dyed with reactive dyes Drimarene Red Cl-5B and Drimarene Blue Cl-BR (0.5% owf) using exhaust dyeing method. The samples were ultrasonically dyed at varied temperature (60, 50 and 40oC) for 60, 50, 40 and 30 minutes and for conventional method at varied temperature but at recommended time, 60 minutes. For optimizing the dyeing behavior, the samples were causticized by pad-batch method and then dyed with ultrasonic technique at varied temperature and time. It has been observed organic cotton fabric dyed using ultrasonic exhaust method at 60oC for 50 minutes gives highest (K/S)?max value, excellent fastness property, deeper dye diffusion and less surface deterioration compared to the conventional dyeing method. Moreover, causticized and dyed sample with ultrasonic technique at 60oC for 30 minutes gives colour strength value almost equal to the conventional recommended dyeing method. Hence, dyeing of organic material using ultrasonic exhaust method saves energy and time