The substantial increase of the atmospheric CO2 concentration over the last few decades has steered toward research on direct air capture (DAC). DAC is one of the mobile-source carbon capture and storage (CCS) processes that is variant from the conventional point-source CCS in terms of easing the CO2 concentration levels and promoting negative carbon emission. We propose here a sustainable material based on the quaternization of bamboo fiber and the implication in DAC. The quaternized bamboo cellulose could adsorb CO2 at a medium relative humidity (RH) of 60-80%, with the efficiency of quaternary ammonium groups over 0.65. The CO2 capacity at higher RH strikingly decreased, which indicates the moisture swing characteristics, and that was further validated by a desorption ratio of 0.70 under humid gas purge. The unique phenomenon that a dry atmosphere (e.g., RH < 20%) is not favored by adsorption was revealed and could be attributed to the hydrophobic feature of the sorbent inherited from natural lignocellulose. The results suggest that quaternized cellulose with a low cost may open up new possibilities for the utilization of moisture-swing CO2 adsorbents in damp circumstances.