A mixture of the trimethylsilyl derivatives of sugar O-methyloximes was separated in a fused silica capillary column. This method permits the rapid and accurate determination of neutral sugars in acid hydrolysates of rice straw and straw compost. The amount of each sugar was corrected by using the regression equation that relates the peak area ratio to the molar ratio of the sugar versus inositol in acid hydrolysates. After hydrolysis in trifluoroacetic acid, xylose was released predominantly from the residue left after the hot-water extraction of rice straw and the compost. The extraction procedures proposed here can be used for the characterization of hot-water soluble carbohydrates, xylan-like hemicellulose, and cellulose. One gram of rice straw contained 1.35 mmol xylose, 0.28 mmol arabinose, and 2.52 mmol glucose. Small amounts of rhamnose, fucose, mannose, and galactose were released from rice straw, whereas ribose was hardly detected. On the other hand, 1 g of a well-matured straw compost contained 0.14 mmol xylose, 0.04 mmol arabinose, and 0.27 mmol glucose; these values were about one tenth of those for rice straw.