Oil and coixenolide are important components of adlay seed (Coix lachrymal-jobi L. var. Adlay) with many beneficial functions to human health. In this work, a novel extraction technique-ultrasound assisted supercritical fluid extraction (USFE)-was studied. Effects of operating conditions on the extraction, including extraction temperature (T), pressure (P), time (t), CO2 flow rate (F) and ultrasonic power (I) were investigated. There are optimum temperatures which gives the maximum extraction yields (EYs) for the supercritical fluid extractions with and without ultrasound. The effect of pressure on EYs for is similar to that of pressure on CO2 density. Based on the yield of extraction, the favorable conditions for supercritical fluid extraction (SFE) were: T at 45 °C, P at 25 MPa, t at 4.0 h and F at 3.5 L/h. While ultrasound was applied as in USFE, the following parameters were preferred: T at 40 °C, P at 20 MPa, t at 3.5 h and F at 3.0 L/h, respectively. The results show that supercritical fluid extraction with the assistance of ultrasound could reduce the temperature, pressure, CO2 flow rate, as well as time used in the process. Compared with SFE, USFE could give a 14% increase in the yield for extracting oil and coixenolide from adlay seed with less severe operating conditions. ; Department of Applied Biology and Chemical Technology