Rapid and highly sensitive detection of iodine gaseous species is crucial as the first response in case of nuclear accidents and nuclear waste clean-up. A robust and user-friendly sensor-based technology that allows online monitoring is highly desirable. Herein, we report the success of using a covalent organic framework (AQ-COF)-based sensor for real-time iodine gas adsorption and detection by the electrochemical impedance spectroscopy (EIS) technique. The sensor exhibits a high sensitivity and a pronounced electrical response to trace amounts of iodine vapor. Gaseous iodine was readily detected with a significant change in resistance (10⁴×) at 70 °C within 5 min exposure to air. Notably, the EIS response is quite chemoselective to iodine over other common species such as air, methanol, ethanol, and water, with a selectivity of 320, 14, 49, and 1030, respectively. A mechanical study shows that the adsorption of iodine can reduce the optical bandgap of the AQ-COF, causing the impedance to drop significantly. This study demonstrates how the adsorption enrichment effect of selective I₂ adsorption by a covalent organic framework can be leveraged to create a highly selective sensor for the direct online electrical detection of radioactive gaseous toxins.