Sea cucumber Apostichopus japonicus juveniles acclimated to different environmental conditions (23, 25, and 27°C combined with 25, 30, and 35 psu) were assessed for tolerance to increasing and decreasing levels of salinity at a rate of 2 psu h -1 . They were also tested for the LS 50 (median lethal salinity) when transferred directly into a series of higher salinity (32-46 psu) and lower salinity (9-25 psu). The CSMax (critical salinity maximum), CSMin (critical salinity minimum), USTL (upper salinity tolerance limit), and LSTL (lower salinity tolerance limit) were positively correlated to the acclimated salinity level but negatively correlated to temperature. The CSMax of A. japonicus was 6.2-10.0 psu higher than the USTL, and the CSMin was 5.5-8.5 psu lower than the LSTL, indicating that gradual changes in salinity resulted in the wide range of salinity tolerance that was observed, but that abrupt changes in salinity resulted in the narrow range of tolerance. Two-way analysis of variance revealed that salinity and temperature had a significant effect on 50% CSMax, 50% CSMin, USTL, and LSTL (P \ 0.001). The information obtained in this study will be valuable for the further development of the sea cucumber aquaculture industry in China.