The invention relates to a micro-reformer using a liquid fuel such as methanol and a manufacturing method thereof. The reformer for producing hydrogen gas from the liquid fuel includes a first substrate having a first grooved path and a catalyst layer, and a second substrate having a second grooved path and a catalyst layer, the first and second grooved paths are overlapped on each other forming a micro-channel. The micro-channel has a fuel inlet, a hydrogen outlet, a reforming section, and a carbon monoxide removing section with heating means disposed therein. Although reduced in size, the reformer allows increased hydrogen emission amount due to increased area of the inner path, and is operable with low power due to effective disposition of a heater. This allows manufacturing at low costs and mass-production via semiconductor process.