Malvae Semen is in use in Korean medicine. The Korean medical doctors use Malvae Semen for inducing diuresis for treating stranguria(利尿通淋), etc. I investigated toxicity, poisoning symptoms, side effects, poisoning treatment and prevention against poisoning of Malvae Semen. The results were summarized as follows: 1.The internal excessive using Malvae Semen can cause mental symptoms such as excitement of mind, hallucination, talking in delirium, etc. 2.If the poisoning reaction of Malvae Semen occur, the medical doctors should stop using Malvae Semen and meet symptoms as they call for attention, etc. 3. In order to prevent against poisoning of Malvae Semen, the patients should keep usage, dosage and notes.