Furfural is consumed in its synthetic condition by several side reactions, thereby generating lots of reaction byproducts. The conventional synthetic process is based on the catalysis of xylose by sulfuric acid. Therefore, a large amount of process waste is generated as the spent acid catalyst in addition to the byproducts. A new process principle is proposed in this paper through which furfural can be synthesized in an environmentally benign way. Furfural was synthesized in its high yields even at the high conversions of xylose by utilizing solid acid catalysts and extracting it from the reaction media with supercritical fluid as soon as it is formed. Sulfated titania and sulfated zirconia were prepared and used as the model solid acid catalysts, and supercritical carbon dioxide was distributed in the reaction media as the extracting solvent. The effects of introducing the supercritical fluid were investigated in depth on the correlation among conversion, selectivity, and yield of the synthesis. The reaction model, proposed by Sako et al., reproduced the extraction effects of furfural by supercritical fluid in fairly good agreements. The supercritical fluid extraction was found to be effective enough to overcome the mass-transfer resistance existing in the solid catalysts.