For the prevention and treatment of the disease, a variety of plants and materials from plants have been used throughout history in the countries over the world. People have a preconceived idea that the medicinal herb is a panacea with a wide safety margin. It seems to be generous to apply traditional medicine to treat patients in most countries, because it has been used for a long time. However, some serious circumstances have been reported after using herbs. Chinese herb nephropathy is well-known toxicity of the medicinal herb. Of course, it is not easy to clarify the causal relation between the herbs and side effect of them. There also has been many problems using medicinal herbs in Korea. Even though the most important thing is the toxicity of the medicinal herbs, only sporadic cases have been reported. No significant cumulative data have been produced until this time. The cause of the side-effect includes toxicities of herb itself and metabolites of herbs, contaminants such as residual pesticides, heavy metals, and adulterated toxic substances etc. To keep the public health in using medicinal herbs, it is very important to establish a system to control the medicinal herbs, including standardization of medicinal herb in producing and distribution, and a system to monitor developing toxicity of the medicinal herbs. For the consistency of the result of monitoring, we can find a way to study the efficacy of the medicinal herbs, and suggest a guideline for using medicinal herbs safely.