An ATR measurement system composed of hollow optical fibers, a trapezoid multi-reflection prism, and a couple of fixed-wavelength QCLs emitting different wavelengths is proposed for non-invasive measurement of blood glucose. To choose a wavelength combination that is appropriate for measurement of glucose absorption, firstly absorption spectra of human lip mucosa measured by using an FT-IR-based ATR system are investigated. As a result, two wavelengths, 1152 cm-1 that coincides with an absorption peak of glucose, and 1186 cm-1 where the glucose absorption becomes minimum are chosen. From numerical simulation using spectral absorptions measured by the FT-IR system, it is found that the differential absorption between the above wavelengths shows a good correlation to blood glucose levels. Finally in-vivo measurement using the ATR system equipped with two single-wavelength QCLs is performed and it is found that the measured optical absorption follows the blood glucose well.