Obesity is a major public health issue, and it is often associated with metabolic abnormalities. Lycium chinense Mill. polysaccharide (LCP) is considered to have antiobesity potential due to its hypoglycemic and hypolipidemic effects. However, the mechanisms associated with its antiobesity effects are still not well understood. In this study, LCP not only inhibited the size and number of lipid droplets but also led to cell death in 3T3-L1 adipocytes through downregulating cyclin D1 expression. LCP effectively decreased body weight in high-fat diet (HFD)-induced obese mice. LCP also decelerated the white adipose tissue (WAT) formation in obese mice and improved their hepatic steatosis. LCP might inhibit fatty acid synthesis and improve β-oxidation and glycolysis by modulating the gene expression of key enzymes of lipogenesis and glycolysis in adipocytes. Therefore, LCP may have antihypertrophy and antiproliferative effects and be used as a daily supplement for weight control.