The reaction of Y-2(SO4)(3) with CS2 was studied using thermogravimetry. Anhydrous yttrium sulfate Y-2(SO4)(3) first decomposes to Y2O2SO4 at temperatures which depend upon the heating rate, namely 550-650 degrees C at 1 K min(-1) and 550-750 degrees C at 5 K min(-1). With increasing temperature, Y2O2SO4 is further deoxidized to Y2O2S, and in this step the heating rate exerts a larger effect than in the first step. This reaction is complete at 700 and 875 degrees C at heating rates of 1 and 5 K min(-1), respectively. The last step involves the reaction of Y2O2S to form delta-Y2S3. Single phase Y2S3 was formed at approximate to 950 degrees C when the heating rate was as low as 1 K min(-1). When the heating rate was increased to 5 K min(-1), a small amount of unreacted Y2O2S was found in the Y2S3 product. The compound YS2-x, which was determined as YS1.85, was stable below approximate to 600 degrees C and decomposed to Y2S3 at higher temperatures. The difference of the present reaction from the reaction of Nd-2(SO4)(3) with CS2 to sesquisulfide.