The leaf of Nelumbo nucifera Gaertn has been used for summer heat syndrome as home remedy in China, and it has been used for the treatment of obesity in traditional medical clinics in China, so we investigated the pharmacological activity of the antiobesity effect of N. nucifera leaves extract. N. nucifera alkaloid (NNA), which is the main component in the N. nucifera leaves. 3T3-L1 preadipocytes and high fat diet (HFD)-induced obese SD rats were treated with NNA, and the effects of NNA on the apoptosis in 3T3-L1 preadipocytes and body weight, as well as plasma TC, TG and LDL-C levels in HFD-induced rats were investigated. The results demonstrated that NNA decreased cell population growth of 3T3-L1 preadipocytes and increased the apoptotic cells in a time-and dose-dependent manner. Furthermore, NNA reduced the body weight, the lee's index, adipose tissue weight, and plasma lipid levels in HFD-induced obese rats. Take together, we demonstrated that NNA can efficiently induces apoptosis in 3T3-L1 preadipocytes, and have further implication in in vivo antiobesity effect.