The absorption spectra of carbon monoxide confined in three aerogel samples with different pore sizes have been recorded within the 4100–4400 cm-1 spectral region at room temperature. The measurements were made using a Bruker IFS 125HR Fourier-transform infrared spectrometer. Lineshift and half-width values for CO were obtained. The influence of pore sizes on dependence of CO line half-width values on rotational quantum numbers was studied.