This standard is developed for the purposes of enforcing the Environment Protection Law of the People’s Republic of China and Radioactive Pollution Prevention and Control Law of the People’s Republic of China, protecting the environment, safeguarding the public health, and setting standards for the environmental monitoring methods. This standard specifies the radiochemical analytical method of caesium-137 in water and the ash of biological samples. This standard is the amended integration of Radiochemical analysis of cesium-137 water (GB 6767-86) and Radiochemical analysis of caesium-137 in ash of biological samples (GB 11221-89). It adopts almost the same analytical methods and principles as the original standards.