Dehydrated castor oil (DCO) is the best known and most widely used of all the oils commonly termed "synthetic" drying oils. DCO imparts good flexibility, rapid drying, excellent color retention, and water resistance to protective coatings. In this study, suitable reaction parameters (reaction time, reaction temperature, catalyst ratio, and pressure) were determined for obtaining DCO from raw castor oil. Reactions were performed at atmospheric pressure with N(2) flow as a sweeping gas and at reduced pressure using two different microwave synthesis unit, Start S and Roto Synth, respectively. Iodine value and hydroxyl value of DCO, obtained at atmospheric and reduced pressure (500 mbar), were determined as 135.8 and 140, and 12.3 and 11.9, respectively, using 4% catalyst (w/w) at 250 degrees C and 20 min reaction time. Fatty acid composition of DCO was determined by gas chromatography analysis to observe the increase of the content of unsaturated fatty acid. Under the applied conditions, dehydration reaction time was decreased from hours (1-2 h) to 20 min using microwave heating system.