Abstract Response surface methodology was used to optimize the xylose production from pinewood sawdust through dilute-phosphoric-acid hydrolysis. The effects of independent variables on xylose yield were investigated, including reaction temperature (75–175 °C), reaction time (0–7.2 h), solution-to-feed ratio (4–20 mL/g), and phosphoric-acid concentration (0–6.67 wt%). Results indicated that the individual factor H3PO4 concentration and the interacting factors including temperature × time, temperature × H3PO4 concentration, and solution-to-feed ratio × H3PO4 concentration were all significant factors. Long reaction time (>5.4 h) and high phosphoric-acid concentration (>5%) showed little effect. Xylose yield increased with increasing temperature up to 125 °C. Higher phosphoric-acid concentration and larger solution-to-feed ratio also increased xylose yield. The coefficient of determination, corresponding analysis of variance, and parity plot indicated that the fitted model was appropriate for the acid-hydrolysis process. The maximum xylose production of 90.95% could be obtained with the reaction temperature of 106.7 °C, reaction time of 4.57 h, phosphoric-acid concentration 4.49 wt%, and solution-to-feed ratio of 12.51 mL/g.