Abstract: The effects of salinity (15, 20, 25, 30, 35) and body weight(2.11±0.60) g, (6.31±0.85) g and (8.80±1.40) g on oxygen consumption rate (OR) and ammonia excretion rate (AR) of Sipunculus nudus Linnaeus were studied using experimental ecology methods. The results indicated that salinity had significant effect on OR and AR, and their interaction also had significant influence on OR and AR. Both OR and AR increased with salinity increment, and reached its peak at salinity 25, then decreased rapidly with salinity increasing. The relationship between OR and salinity can be represented by the quadratic equation y=-ax²+bx-c, where a ranges from 0.030 to 0.044, b ranges from 1.525 to 2.252, c ranges from 11.824 to 20.132. The relationship between AR and salinity was similar with OR and salinity, however, a ranges from 0.009 to 0.012, b ranges from 0.455 to 0.593, c ranges from 4.369 to 5.275. The O/N value ranged from 4.06 to 14.28. The study showed that S. nudus Linnaeus can adapt to the low salinity and high salinity environment by adjusting physiological metabolism, and the salinity 25 might be the optimum for the growth.