We developed a novel technique to investigate local pH distribution on a chip using patterned hydrogel film made of UV photosensitive resin. The hydrogel is first patterned by photolithography in any shape on a glass, and later functionalized with the pH indicator, for example, Bromocresol Green (BCG). The hydrogel is polymerized by UV-ray illumination (300-400 nm) on the glass substrate, which is spin coated with the water-soluble prepolymer solution, and immobilized on the glass surface. Unexposed part can be removed easily by water. The hydrogel is hydrophilic, transparent, biocompatible, and is impregnated with the BCG. Then, the Polydimethylsiloxane (PDMS) microchannel is assembled and bonded on the functionalize surface. In this way, we can make patterned pH sensitive surface in the microchannel. Local pH is measured from the color of the hydrogel impregnated with BCG based on the calibrated color information in YCrCb color space. We succeeded in measuring local pH distribution in the microchip.