A steam plasma jet (SPJ) by using both water and 1,4-dioxane aqueous solution (DAS) as working medium was injected into contaminated water to decompose 1,4-dioxane. The optical emission spectroscopy analysis showed that the formation of the excited species CH * and C * 2 depended on the concentration of 1,4-dioxane. The influences of SPJ gas temperatures for different working mediums were discussed. The 1,4-dioxane decomposition was enhanced when DAS was used as working medium and SPJ was injected into DAS. Synthesis gas (a mixture of H2 and CO) and CO2 were the main products in gaseous effluents.