In order to study effects of serum leptin level on energy metabolism, we measured body mass, serum leptin levels, energy intake, rest metabolic rate (RMR), nonshivering thermogenesis (NST) in Eothenomys miletus under cold acclimation (5℃) or rewarming (30℃). Cold acclimation induced increases in RMR, NST, energy intake. Those measurements decreased after rewarming. Body mass, serum leptin levels decreased during cold acclimation treatment and increased after rewarming. Serum leptin levels were positively correlated with body mass and negatively correlated with RMR, NST and energy intake. These results suggest that body mass, energy intake, thermogenic Capacity in E.miletus has a strong phenotypic plasticity. Serum leptin participated in the regulation of energy balance and body mass in E.miletus during cold acclimation and rewarming.