Nanocomposites are hetero materials made up of at least one nanoscale phase called a "nanofiller" that is spread in a second phase called a "matrix" to combine the unique features of its ingredients. Contemporary uses for nanocomposites are expanding constantly, and they are being used in many different industries. Nanocomposites are used in a variety of products, such as solid polymer electrolytes for batteries, impellers and blades, oxygen and gas barriers, food packaging, thin-film capacitors for computer chips, and fuel tanks and engine parts. As drug - delivery techniques, anti-corrosion shield coatings, UV protection gels, oils, scratch-free paint, new scrape resist materials, new fire-retardant materials, superior fibres and films, etc., they also find extensive application. Extensive use of these composites led to the discloses of these stuffs into the environment and properties of these materials are greatly influenced by the presence of pollution. The physico-chemical properties of these nanocomposites are very important for predicting their fortune and behavior in the environment and their toxicity to living organisms. Limited data on the ecotoxicity of these materials are available and even those are confined to a few organisms like bacteria, algae, invertebrates, fishes and mammals. Detailed studies on the adsorption, distribution, metabolism and excretion on higher organisms is the need of the hour. Presently the environmental risk assessment of nanomaterials is being performed using the existing methodologies and modification of the methodologies are required. This review summarizes the toxicity of nanocomposites and the current toxicological tests carried out.