Abstract: Objective: To optimize the preparation process of polysaccharides from Lycium ruthenicum, analyze the monosaccharide composition and evaluate its pancreatic lipase inhibitory activity in vitro. Methods: Ultrasound-assisted aqueous two-phase extraction method was employed. Taking the overall evaluation value of polysaccharide recovery and extraction rate as the evaluation index, on the basis of single factor experiment, response surface analysis was conducted to optimize the extraction process. The composition of monosaccharides was studied by high performance liquid chromatography with pre-column derivatization. The pancreatic lipase inhibitory activity of Lycium ruthenicum polysaccharides was evaluated by p-nitrophenyl palmitate method. Results: The optimum extraction conditions: Ethanol-ammonium sulfate system, ethanol concentration 30.89%, ammonium sulfate concentration 17.00%, extraction temperature 49.05 ℃, extraction time 81.85 min, liquid to material ratio 29.80 g/g. At this time, the predicted total evaluation value was 0.9242, and the extraction and recovery rates were 104.76 mg/g and 96.96%, respectively. Lycium ruthenicum polysaccharides were composed of monosaccharides such as mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose and arabinose, with the relative molar ratios of 4.92:0.29:4.80:0.40:9.69:44.79:17.04:18.06, respectively. The IC₅₀ value of Lycium ruthenicum polysaccharides inhibiting pancreatic lipase was 1.51 mg/mL. Conclusion: The preparation process of Lycium ruthenicum polysaccharides optimized by response surface methodology was stable. The detection method of monosaccharide composition was accurate and reliable. Lycium ruthenicum polysaccharides had good pancreatic lipase inhibitory activity in vitro. The results would provide a basis for the further development and utilization of Lycium ruthenicum polysaccharides.