In this study, we evaluated the toxicity of 16 veterinary drugs approved in Japan (antimicrobial substances, antiparasitic agents, and disinfectants) using a fish acute toxicity test, Daphnia swimming inhibition test, algae growth inhibition test, and earthworm acute toxicity test. Test organisms included Oryzias latipes, Daphnia magna, Pseudokirchneriella subcapitata, and Eisenia fetida. The tests were performed in accordance with the Organisation for Economic Co-operation and Development guidelines for testing chemicals. In the Globally Harmonized System of Classification and Labelling of Chemicals, when the EC/LC₅₀ value of a substance is < 1 mg/mL, then the substance is classified as Category 1, or highly toxic to aquatic organisms. The results of the present study indicate that the toxicity of tylosin phosphate, lincomycin, oxytetracycline chloride, and chlortetracycline to algae; that of ivermectin to crustaceans and fish; and that of didecyldimethylammonium chloride to all organisms examined should be classified as Category 1. In terrestrial organism, weak toxicity was observed with ivermectin, fenbendazole, and didecyldimethylammonium chloride. These data are considered to be valuable data for actually knowing the toxicity of veterinary drugs, in particular, since there is hardly any data following the guidelines using Eisenia fetida. Our results also suggest that the environmental risk of the tested veterinary drugs might be low at present researched environmental levels in river. In addition, our data indicate that the possibility of many veterinary drugs adversely affecting the environment is low if they are properly used.