Abstract: Significance of plasticity in energy budget and development of animals in response to variations of food availability was examined in weaned male KM mice that were acclimated to a random food deprivation (FD) for 4 weeks, and then refed ad libtum for another 4 weeks. Food intake was determined using a food balance method. Basal metabolic rate (BMR) was measured using a closed-circuit respirometer. Food intake increased significantly on ad libitum day in FD mice, but BMR and activity decreased. FD mice also had a significantly lower weight in carcass and gonadal gland than controls after 4 weeks of FD. All the above parameters recovered to the levels of controls after 4 weeks of ad libitum refeeding, indicating a significant plasticity. In addition, the group difference in fat content was not significant. These results suggest that animals can compensate for unpredictable lower food availability by an energetic strategy, including an increase in food intake and a decrease in energy expenditure associated with BMR and activity, and decrease in carcass mass thus reduced energy spent on maintenance, but not including the changes in body fat. Development is affected significantly by lower food availability but recovers to the normal level when food is plentiful. Finally, plasticity in energetic budget and development play important roles in animals under unpredictable variations of food availability.