Supercritical water is a promising reforming media for the direct production of hydrogen at high pressures with a short reaction time. In addition to being a dense solvent, supercritical water also participates in reforming reaction. In this work, high-pressure hydrogen is produced from ethanol by reforming over a Ru/Al2O3 catalyst with low methane and carbon monoxide formation. Experiments were conducted in a continuous tubular reactor to study the effects of temperature, pressure, residence time, and water-to-carbon ratio on the H-2 yield. Hydrogen formation is favored at high temperature and at high water-to-ethanol ratio. The formation of methane can be suppressed by operating at an optimal residence time, high reactor temperature, and a low feed concentration of ethanol. Excellent conversion in reaction time as short as 4 s is achieved. Pressure has a negligible effect on hydrogen yield above the critical pressure, and for less than 10 wt % ethanol concentration in the feed, there was negligible coke formation. On the basis of the products obtained, a reaction mechanism is discussed. An activation energy of 65.3 kJ mol(-1) was observed.