The water-gas shift reaction (WGSR) using a pure steam plasma with CO as the reactant was accomplished in this study. The steam plasma generated by microwaves at an atmospheric pressure provides highly active species and a high-temperature plasma flame at about 6000 K, which enhances the chemical reaction rate and eliminates the need for catalysts. We stably generated the steam plasma with the conditions of the power at 3 kW and the steam flow rate at 27 L/min with swirl flow. The energy efficiency and CO conversion were estimated. Using a cylinder type of reactor, 40 vol % hydrogen was produced at a given steam/carbon (S/C) ratio. To improve the stability and residence time in the reaction, we designed a reverse vortex reactor (RVR). Using a RVR, an average of 36 vol % hydrogen was produced and the stability of steam plasma was highly increased.