The bioconversion of xylose to xylitol by the yeast Candida guilliermondii FTI 20037 was evaluated under different nutritional conditions using rice straw hemicellulose hydrolysate. Statistical designs were used to determine the fermentation medium composition. Ammonium sulfate and rice bran have been identified as required nutrients in the hydrolysate since there was a significant interaction between them. In the presence of both nutrients, the xylitol yield factor (Yp/s) and volumetric productivities (Qp) were 0.68 gig and 0.54 g/L.h, respectively.