The safety and toxicity of chemicals given first to animals and finally to humans are generally estimated with a method of safe coefficient, which is scientifically a way lack of grounds. To make a change of the old method, we designed a Physiologically Based Pharmacokinetics Medel for the estimate of safety and toxicity of chemicais. As an example,p-nitrophenol sodium (PNP-Na) is used in the research work. Studies of the PNP-Na pharmacokinetics in bodies of rat as well as humans are made, and possibilities of making use of the Model in the estimate of safety and toxicity of chemicals are discussed. The safety and toxicity of chemicals given first to animals and finally to humans are estimated with a method of safe coefficient, which is scientifically a way lack of grounds. the estimate of safety and toxicity of chemicais. As an example, p-nitrophenol sodium (PNP-Na) is used in the research work. Studies of the PNP-Na pharmacokinetics in bodies of rat as humans are made, and possibilities of making use of the Model in the estimate of safety and toxicity of chemicals are discussed.