We have proposed a new application of an AWG for a compact planar spectroscopic sensor to meet both conditions for miniaturization and high-wavelength resolution in the sub-nanometer order. A liquid sample under test is poured into a groove (optical path length, 70μm: groove depth, 110μm) in the first slab region of the AWG. A preliminary experiment was carried out using water solution of sodium acetate with the fabricated near-infrared AWG sensor. Concentration of the sodium acetate solute could be determined with the average accuracy of ±0.25 wt%. As the next step of AWG-based sensor, we designed and fabricated a compact spectroscopic sensor using an AWG with an insertion loss of 4dB in the visible wavelength. For improving the sensitivity of visible AWG spectroscopic sensor, the optimal design of a groove for the liquid sample was carried out in consideration of the refractive index and transmittance of the chlorophyll a and b as various environmental indicators. We succeeded in discriminating chlorophyll solutions using the AWG sensor. And we obtained a transmittance difference of 1.4dB which is two times higher than that in the conventional scheme (0.7dB) by absorbency change of 1.0 (optical path: 1.0mm). From these theoretical and experimental investigations using a visible AWG, a compact AWG-based spectroscopic sensor has been confirmed to be effective in acquiring body information in bio-medical fields.