Xylitol production by the yeast Candida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate under different conditions of initial pH and nitrogen source. Xylitol production was significantly affected (p < 0.05) by the nitrogen source, pH, and the interaction between these factors. The best yield and productivity were observed at initial PH of 5.3 in medium containing ammonium sulfate as nitrogen source. Under these conditions, the xylitol yield factor (Y-p/s) was 0.68 g/g and volumetric productivity (Q(p)) was 0.51 g/L.h.