A patterning method of micro-flow shapes with ribs along both sides of the micro-flow path has been developed using synchrotron radiation (SR) and double x-ray masks in this study. By setting the alignment of the masks precisely, the pattern with ribs along the both sides of micro flow path without position gaps was able to be exposed on a polymethylmethacrylate (PMMA) plate successfully. A nickel (Ni) mold part was made by electroforming nickel on the patterned PMMA plate, and PMMA microfluidic device was produced using this Ni mold part and injection molding technique. The effect of the ribs for bonding with a cover plate was confirmed in comparison with that of a conventional plastic microfluidic device.