Effect of copper on mysids is investigated for Peter the Great Bay (Japan Sea) in July 2006 and August 2007. High concentrations of Cu2+ are dangerous for biota of the coastal waters. Mysids (small crustaceans) are the best test organisms for evaluation of pollutants toxicity and for bioassay of polluted waters because of their wide spreading in the coastal waters, short life cycle, easy collection and cultivation, and high sensitivity to water quality. Two mysid species - Neomysis mirabilis and Paracanthomysis sp. are common for shallows of Peter the Great Bay in May-October. For the experiment, the mysids were collected in a shallow area from the surface layer (0.05-100 cm). Survival rate was examined for their females with length 12-14 mm ( N. mirabilis ) and 13-14 mm ( P. sp.), for that 5 individuals of each species were transferred from big aerated tanks into 600 mL glass jars containing 500 mL of different test solutions prepared by adding the necessary amount of copper sulphate, CuSO4 • 5H2O dissolved in bidistilled water to the seawater with temperature 20-22 °C and salinity 32-33 ‰. The copper ions concentration in the tested solutions was measured at the beginning and at the end of each experiment using Nippon Jarrell Ash AA-855 atom-absorption spectrophotometer. The mysids were not fed during the testing. Each test was repeated three times for each Cu concentration and for the control sample without copper. So, survival of 15 individuals was examined for each of 5 tested concentrations of Cu, that allowed to get the dose-effect equations with good significance. Some mortality of tested animals was observed in control groups, too; this effect was accounted by Abbott correction. Probit-analysis is used for processing of the results obtained in 96 h experiments. Paracanthomysis sp. is less tolerant to impact of Cu pollution, as compared with Neomysis mirabilis : lethal concentrations for 96 h exposure were LC0 0.8-0.9, LC10 1.4-1.5 and LC50 3.1-3.2 μgCu/l for P. sp . (sampled in July 2006 and August 2007) and LC0 3.4, LC10 4.8, and LC50 8.1 μgCu/l for N. mirabilis (sampled in July 2006). Moreover, Paracanthomysis sp. tolerance to copper is similar or lower than the tolerance of other cited tests-objects, as molluscs and sea urchins, though they have a wide range of LC50 for copper, depending on the species, life stage, and conditions of the experiment. Variation of tolerance among species could be reasoned by differences in their size and physiology; besides, young organisms are usually less tolerant to pollution than adults. In Peter the Great Bay, a noticeable negative effect of Cu on mysids is observed only in local areas of high anthropogenic pollution in the Amur, Ussuri, Nakhodka, and Posyet Bays where their survival is lowered.