An efficient highly regioselective C5-H direct iodination of indoles is reported herein for the first time. Due to the versatility of aryl iodides, the method offers a general and practical access to the C5 functionalization of indoles. The approach features mild reaction conditions, good tolerance of functional groups, and more crucially, no metal involved in the reaction, thereby benefitting the late-stage decoration of medicinal molecules. A mechanistic study showed that the current iodination reaction proceeded via a radical pathway.