Design and fabrication of micro mixing cells and detection cells were investigated. Glass micro mixing cells with island structures among channels were fabricated using sand blaster methods. Depth and width of mixing channel were 200 mu m and 180 mu m and island size was 90 mu m by 90 mu m. Two 45 degrees mirrors surfaces faced on each other in one detection cell which were fabricated by silicon anisotropic etching using 20% TMAH (Tetramethylammonium hydroxide) solution with 20% or 30% IPA (iso propyl alcohol) at 80 degrees C, respectively. Up side glass wafer for mixing cell and down side silicon wafer for detection cell were bonded using anodic bonding method at 350 degrees C, -600 V and 300 N. Synthetic indophenol was injected at inlet and moved to the detection cell through the mixing channel. HeNe laser of 632.8 nm was focused on one side of a 45 degrees mirror, and passed through indophenol solution until the other side of a 45 degrees mirror. The light of 632.8 nm was absorbed in indophenol solution between two 45 degrees mirrors at detection cell. By the Beer-Lambert's law, indophenol concentration could be calculated from the measured result of the absorbance.