Aestivation is defined as a period of dormancy or inactivity allowing animals to survive during an extremely hot and/or dry season. This phenomenon has been observed from various animals including earthworms, snails, bivalves, sea cucumbers, lungfishes and amphibians. Apostichopus japonicus is a temperate sea cucumber and known to aestivate when water temperature rises over 20 ℃ to 24.5 ℃. We measured effects of aestivation on energy utilization (i.e., energy distribution in growth, feces, respiration and excretion)of A. japonicus with two different body sizes (large (134.0±3.5)g and small (73.6±2.2)g) at water temperatures between 10 ℃ to 30 ℃ with 5 ℃ intervals. The data indicated that water temperature, body size and/or their interaction exerted significant effects on energy ingestion. In particular, water temperature was the main factor influencing energy allocation of A. japonicus. Noticeable variation in the energy utilization of sea cucumber was also observed in this study. During non-aestivation period, energy deposition in growth was lower and the energy loss through feces accounted for the majority of the ingested energy. Under threshold temperature, the energy intake became reduced and energy deposited in growth became negative. During aestivation, sea cucumber discontinued energy intake, resulting in weight loss. Our study suggested that the ecological implication of aestivation in this species could be a mode of energy saving during long-term hot period.