Obesity is a worldwide health problem due to its epidemic proportions and high risk for other metabolic disorders, such type 2 diabetes, cardiovascular diseases and certain cancers. It is generally accepted that a chronic low-grade inflammatory state is at the pathogenic core of obesity. High-fat diet-induced obesity features of hyperleptinemia, hyperinsulinemia, fat deposition, glucose intolerance, central and peripheral inflammation, as well as central and peripheral leptin resistance and hypothalamic leptin signaling compromised. Obesity also features of the impairment of prefrontal cortex, and impairment of leptin-induced regulation of brain-derived neurotrophic factor (BDNF) expression and synaptogenesis, which has been considered to be associated with the incidence of neuronal degenerative diseases, cognitive decline, and depression. Some plant-derived triterpene saponins are anti-inflammatory and inhibit the NF-κB signaling. Those triterpene saponins are potential therapeutic agents for the obesity-associated inflammation to be determined. Natural extracted triterpene saponins, ginsenoside Rb1 and teasaponin, are used in this PhD research project. Ginsenoside Rb1, extracted from Ginseng, has anti-inflammation effect and anti-obesity effect. However, it is unclear whether it has the effect of anti-obesity-associated inflammation and whether it can address the above listed features issue of obesity. Teasaponin is an active compound of tea extract, has been demonstrated to ameliorate obesity, reduce inflammation and improve central leptin sensitivity in obese mice in our previous study. Tea consumption improves cognition and increases brain activation in the prefrontal cortex. However, little is known on the ability of teasaponin on recognition memory and its effect on leptin signaling in the prefrontal cortex of high-fat diet-induced obese mice.