Salinity tolerance, temperature tolerance and combined effects of temperature and salinity on survival were investigated in the laboratory on the copepod, Pseudodlaptomiis ardjuna from Bombay coastal waters. Experiments on salinity tolerance were conducted at salinities from 35%„ (taken as 100% sea water) to 0%^ (fresh water) at ambient room temperature. The copepod could tolerate salinity down to 37 % sea water when subjected to sudden exposure. Salinity acclimation increased the salinity tolerance and it could tolerate dilutions as low as 10% sea water after gradual acclimation. The upper and lower lethal temperatures were found to be 35°C and 8°C respectively, in full strength sea water. Investigations on the combined effects of temperature and salinity were carried out by subjecting the copepods to various combinations of salinities and temperatures within the tolerance limits. The animal exhibited better survival in various salinities at higher range of temperature. The experimental results were compared with the field observations and the effects of salinity and temperature on the distribution of P. ardjuna are discussed in the light of the above findings.