Temperature measurement of aqueous solution in a micro-fluidic chip by using near-infrared spectroscopy is presented. The principle is based on the temperature dependence of the v_2 + v_3 absorption band of water. Absorbance spectra for two areas in 50-μm thick water in a temperature controlled Y-channel were measured simultaneously by two photospectrometers. The spectra indicated the temperature difference between the two areas. The images of absorbance at 1905 nm corresponding to temperature images were obtained by using a near-infrared camera and narrow bandpass filter. Calibration measurements on water in the Y-channel from 24.0℃ to 46.0℃ demonstrated a temperature coefficient of 4.5 x 10^<-4>℃^<-1>. Finally, temperature distributions caused by a heating wire were visualized.
