Abstract: The joint toxicity of copper and cadmium to tadpole is studied in acute tests．The results show that the LC₅₀ of Cu²⁺ to tadpole is 0．201 mg／kg，0．138mg／kg and 0．118 mg／kg in 24h，48h and 96h，respecitively；and the LC₅₀ of Cd to tadpole is 32．1 mg／kg，23．3mg／kg and 18．9mg／kg in 24h，48h and 96h，respectively．According to the addictive index method of marking，the addictive index(AI)of Cu²⁺ and Cd²⁺ to tadpole is 1．03，1．12 and 1．20 in 24h，48h and 96h，respectively．The results show synergism action．