Abstract: Using infra-red gas analyzer and tube-type air sampling unit, the SO₂ concentrations at different heights are measured in natural and secondary korean pine-broad leaved mixed forests on Changbai Mountain.CO₂ in forest stands changes diurnally:in canopy, it decreases during day time and increases at night. CO₂ in forest stands are supplied both from forest floor and atmosphere above canopy. Higher concentration of CO₂ near ground surface provides better CO₂ environment for regenerated seedlings than in upper layers.