Cinnamomi Cortex is in use in the Korean medicine. The Korean medical doctors use Cinnamomi Cortex for warming the middle-jiao(溫中), and clearing away cold(散寒), and restoring yang(助陽), etc. We investigated toxicity, poisoning symptoms, side effects, poisoning treatment and prevention against poisoning of Cinnamomi Cortex. The results were summarized as follows： 1. The main ingredients of poisoning are cinnamic aldehyde, etc. The ingredients of poisoning from Cinnamomi Cortex mainly can cause stimulating symptoms on digestive system, urinary system and nervous system, etc. 2. The representative methods of poisoning treatment in the western medicine are washing out the stomach, promotion of vomiting, causing diarrhea, enema, supplies of grape sugar and symptomatic treatment, etc. 3. The representative methods of poisoning treatment in the Korean medicine are removing heat(淸熱), nourishing yin(養陰), and relieving thirst(止渴), etc. And Korean medical doctors should meet symptoms as patients call for attention. 4. In order to prevent against poisoning of Cinnamomi Cortex, the patients should keep usage, dosage and notes.