Abstract: An optoacoustic analyzer which allows the light from a laser resonator to enter a differential cell assembly can not provide accurate measurement of a specific component of ultralow concentration because the laser light, as it passes through the sample chamber and reference chamber, is absorbed to cause significant attenuation and the adverse effect of a low concentration of an inhibitory component in the fluid sample can not be effectively eliminated. Further, this type of anaylzer receives the laser light at the detector after it has passed through mirrors, and therefore, only few percents of the light within the resonator reaches the detector, thus providing only low sensitivity. To solve these problems, the differential cell type, light transmitting, optoacoustic analyzer of this invention has the sample chamber and reference chamber disposed on the beam path between the resonating mirrors in the gas laser resonator.