This paper presents an optical transcutaneous pCO2 gas sensor and analyzer using a noninvasive method. The basic principle of the pCO2measurement method adapts Beer- Lambert’s law and the embodied system uses the nondispersive Infrared (NDIR) method. Since CO2 gas reacts to a 4.3 m wavelength, this wavelength is selected using an optical filter, and used energy decrease by molecule oscillations. The CO2 concentration is then measured by a mass flow controller (MFC) using basic steps, instead of collecting pCO2 gas by inflicting heat on the outer skin. The measuring system consists of an IR lamp, optical filter, optical reaction chamber, pyroelectric sensor, and a signal processing part. To make the sensor system portable, the length of the optical reaction chamber is mini- mized to 1 mm using a Si wafer based on MEMS technology. When CO2 gas is injected into the optical reaction chamber, a result of 4.3 mV was confirmed when using a photoreaction path of 1 mm with a CO2 gas reaction. The response time of the system was within 2 s, which we consider to be relatively rapid.