Effects of anthropogenic pollution on aquatic environment have been concerned because some of pollutants have toxicities to aquatic organisms including immunotoxicity. Because immune system is responsible for biological defense and maintenance of good health, toxic effects of chemicals on immune system would decline health condition of organisms. Aquatic organisms which live in polluted areas were reported to be occurred immunotoxic symptoms such as histological changes of lymphoid tissue, changed immune functions and immune cell populations, and changed host resistance to infection pathogens. In addition, aquatic organisms are always thought exposed to pathogen (bacteria, virus, fungi, etc.) via water. Therefore, suppressed immune system by contaminants should increase infection risk. Furthermore, it poses ecological risks such as extinction. In this review, we introduced immunotoxic effects of pollutant contaminants on aquatic organisms including aquatic invertebrates, fish, amphibian and marine mammals, and discussed posed-effects on aquatic population and ecosystem.