To investigate the toxic of herbs used in <Bangyakhappyeon; 方藥合編>, the author analyzed herbs with toxic recorded in <Imsangbonchohak; 臨床本草學>, <Jungyakdaesajeon; 中藥大辭典>, after searched toxic herbs literarily. Herbs with toxicity recorded in both <Imsangbonchohak> and <Jungyakdaesajeon> were total 17 species, and recorded in <Imsangbonchohak> were total 13 species, and recorded in <Jungyakdaesajeon> were total 12 species. The major cause that herbs generates a side effect in a human body is implicit use and abuse, inadequate processing the herbs, use of quack medicines of herbs and clinical use which is improper in symptoms and internal use, differences of constitution. The major toxic component in herbs is an alkaloid, essential oil and hydrargyrum (Hg), and the main invasion route of toxic herbs in human body is the liver, kidney, lungs, and gastrointestinal tract.