Trioxane extraction with supercritical fluids was directly applied to an actual trioxane synthesis system. The reaction/extraction was conducted for an aqueous solution of formaldehyde with an acid catalyst in the presence of supercritical fluid. It was found that carbon dioxide is the best extractant and a trioxane solution at a concentration of more than 40% was obtained by one pot with supercritical fluid extraction from aqueous formaldehyde and a catalyst. Study on the reactive extraction by supercritical carbon dioxide fed continuously revealed that the larger vapor/liquid phase ratio is preferable, and the optimized reaction temperature is 373 K.