Using atomic emission spectrometry, it is difficult to achieve high-sensitivity analysis of chlorine, due to its high excitation energy. Only 5% of the total sample volume contributes to the emission intensity, using a nebulizing system of inductively coupled plasma atomic emission spectrometry (ICP-AES). In this study we propose a new oxidation vaporization method, based on the introduction of gaseous chlorine into the plasma. High-sensitivity chlorine analysis has been achieved by this method, due to an almost 100% conversion of chlorine dissolved in the sample into the gaseous state. As a result, the sensitivity improvement achieved, and this new method can be used with the commercial introduction system, with a 20-times improved sensitivity for chlorine, compared with the typical nebulizing system. Results obtained by the new method were confirmed using mineral drinking water and river water. The measured values were almost identical to those obtained by ion chromatograph, while the measurement took only one minute.