In our preceding study, we clarified that liquids having similar molecular sizes to ethanol were mainly adsorbed onto lignin among the major constituents of wood. This suggests that most micropores or adsorption sites loosely hydrogen-bonded to each other, which are accessible to these liquids, exist in lignin. In the present study, to examine micropores in wood and lignin, micropore distribution was measured by CO2 gas adsorption at ice-water temperature (273 K). Dry samples prepared by gradual delignification from wood meal were used as adsorbents. The pore-size distributions were determined by analyzing adsorption isotherms using the Horvath-Kawazoe method. It was found that the number of micropores decreased with the decrease in residual lignin, and micropores were hardly found in cellulose and hemicellulose. It is considered that most micropores smaller than 0.6 nm in wood exist in lignin.