Optoacoustic measurement of the absorption line shape is carried out for the determination of the homogeneous linewidths and the saturation intensities of a CH3I molecule for a 10‐&mgr;mP(32) CO2laser line. By fitting the numerically calculated Voigt function to the experimentally obtained absorption line shape, we find two absorption lines separated by 90 MHz. The measurement of the pressure dependence of the homogeneous linewidth at pressures lower than 0.8 Torr shows that the rate of increase of the homogeneous linewidth is not linear but larger at lower pressure than that at higher pressure. The natural linewidth of 12 MHz is obtained by extrapolating the experimentally obtained linewidth curve toward zero pressure, and also the pump saturation intensities at the line centers of the CH3I absorption line and CO2laser line are found to be 1.0 and 2.5 W/cm2, respectively.