Following a radiological or nuclear event, radioactive iodine may be get into the body through respiratory or gastrointestinal systems. In the contaminated cases with radioactive iodine, the radioactive iodine absorbed by the thyroid can injure the gland. Because of the carcinogenic effects of its radiation, there is a significant public health risk in the event of exposure to radioactive iodine. On other hand, due to stable (non-radioactive) iodine acts to block radioactive iodine from being taken into the thyroid gland, it can help protect this gland from injury and following side effects. In this query, potassium iodide (also called KI) is a salt of stable iodine in a medicine form which is recommended to use sine many years ago. With effective planning and the use of stable iodine prophylaxis, accompanied with other protective implementations, this risk is mostly avoidable. This book contains information such as iodine and physiology kinetic , exposure risk to radioactive iodine, how to use stable iodine in this events , complications attributed to stable(non-radioactive) iodine and also at last chapter the final recommendation published by WHO is included.