In this study, a CO2 separation membrane was prepared by blending polyvinyl alcohol (PVA) and a water-absorbing agent. The effects of the blend composition and the addition of amine-based additives on the separation performance were examined. Membrane preparation by blending PVA and two types of water-absorbing agents promoted the permeation of CO2 and He, while selectivity of CO2 relative to He was slightly decreased. The addition of amine-based additives to the membrane improved the pressure resistance when pressurized from 0.1 to 0.7 MPa at 60 degrees C, and therefore also improved the separation performance. Changing the combination of PVA and the two types of water-absorbing agents during the preparation of the membrane materials led to a further enhancement of the separation performance. Thus, in this study, a CO2 separation membrane with a high separation performance and a pressure resistance of up to 0.7 MPa at 60 degrees C under humidification was prepared.