Growth performance, oxygen consumption rate and biochemical composition of young sea cucumbers were studied at constant and fluctuating temperatures. Groups of young sea cucumber, Aposticchopus japonicus, were reared at fluctuating temperatures of 15?2, 18?2 , 21?2℃ and others were reared at constant temperatures of 12, 15, 18, 21 and 24℃ as controls. Specific growth rates （SGR） were measured under different treatments. Results showed that temperature had significant effects on the growth of sea cucumber. At constant temperatures, growth of young sea cucumbers increased with the increasing of temperature from 12 to 18℃. The subsequent increase of temperature led to the comparative deceleration of the growth rate. Therefore, the appropriate temperature for the growth of sea cucumber was from 12 ℃ to 21℃, and the thermal optimum for growth was about 18℃. Within the ecological tolerance range for the species, the growth rate in fluctuating temperature groups increased compared to the growth rate in the control groups with a constant temperature equal to the average oscillating one. SGR significantly decreased when the temperature fluctuating occured around 21℃. Analysis of covariance （ANCOVA） was used to test the relationship between temperature and body composition of young sea cucumber. The effects of different temperature treatments on body contents of crude protein, crude lipid and energy of sea cucumber were significant. The contents of crude lipid of young sea cucumber reared at fluctuating temperatures decreased compared to those reared at constant temperatures. Among three constant temperature groups, oxygen consumption rates of sea cucumbers increased along with the increasing of temperature treatments. However, there were no significant differences among oxygen consumption rates of sea cucumbers under three constant temperature treatments （ P 〉 0.05 ）. In three fluctuating temperature groups, oxygen consumption rates also increased along with the increasing of temperature treatments. The oxygen consumption rate of sea cucumber in 21＋2℃ was significantly higher than that in 15?20℃（ P 〈 0.05）. Temperature fluctuation enhanced the oxygen consumption of sea cucumbers in the 18?20℃ and 21?2℃ when compared to rates of animals subjected to constant temperattLre. However, the differences of oxygen consumption rates between fluctuating temperature treatments and constant temperattLre treatlnents were not significant （ P 〉 0.05）. Temperature in the sea cucumber culttLre pond can be controlled in the range of 15-18℃, and with a fluctuating amplitude of ＋2℃. By this kind of temperature control mode, growth of young sea cucumber will he accelerated.