Salinity is an important environmental factor in aquaculture that has significant effects on the growth and digestive physiology of aquatic animals. In the system of an aquatic animal digestive enzymes play a crucial role in the nutrient absorption and growth performance. In this study we investigated the effects of low salinity (16, 18, 20, 22 and 24) on the growth and activities of digestive enzymes in sea cucumbers (Apostichopus japonicus) of three different sizes (28.37±3.21 g, 7.52±1.25 g, and 2.03±0.68 g). The results showed that low salinity had remarkable impacts on the growth and digestive enzyme activities in sea cucumbers. The SGR of all three types of sea cucumber increased along with the increase in salinity, and it reached the lowest value at salinity 16 when the animals failed to stretch normally, crept at the bottom of the tank, and almost stopped the food intake. The lowest SGR was significantly different from the control (P<0.05). We also observed that the SGR reached the highest value at salinity 31. In the salinity range of 16−24, the activities of digestive protease, amylase and lipase all increased as the salinity rose. The protease activity of sea cucumbers reached the highest value at salinity 24, which was not significantly different from the control (P>0.05). Small sea cucumbers (2.03±0.68 g) showed no difference in the protease activity between salinity 20 and 22. Activities of amylase were not different between salinity 20, 22 and 24. For the medium-sized sea cucumbers (7.52±1.25 g), the amylase activity increased when the salinity rose from 22 to 24 (P<0.05). The lipase activity of large sea cucumbers (28.37±3.21 g) significantly increased when the salinity rose from 20 to 22, while it was elevated when the salinity rose from 22 to 24 (P<0.05) in small sea cucumbers (2.03±0.68 g). However, when the salinity was higher than 24, the activities of digestive enzymes increased as the salinity reduced. At the same salinity sea cucumbers of different sizes showed no variation in the activities of digestive enzymes. Our studies on the activities of the three enzymes at low salinity will provide reference for the salinity control in the aquaculture of sea cucumbers.