Abstract: This study screened several common economic algae to optimize the extraction process of β-1,3-xylan and analyze its monosaccharide composition. The extraction process of crude xylan was optimized by alkaline extraction method, and the monosaccharide composition of crude xylan was identified by a specific enzymatic method using Caulerpa lentillifera as the main raw material. The effect of extraction time, solid-liquid ratio and NaOH concentration on the yield of crude xylan was optimized with a single factor tests followed by three-three level orthogonal experiment to study the optimal extraction conditions of crude xylan. The results showed that the extraction rate of crude xylan was influenced by the following factors: Extraction time>material-to-liquid ratio>NaOH concentration. The optimum extraction process was: Extraction time of 3 h, NaOH concentration of 2.5 mol·L⁻¹, feed-to-liquid ratio of 1:100 g·mL⁻¹, and the yield of crude xylan was 28.1%±0.6%. The enzymatic products were determined by thin-layer chromatography, which showed that the crude xylan extracted from Caulerpa lentillifera was β-1,3-xylan and the monosaccharide fraction was β-1,3-xylose.