The air quality in downtown area is seriously polluted by various kinds of air pollutants. For this reason, many drivers recirculate theindoor air instead of introducing new fresh outdoor air in downtown area. However, in this case, CO₂ concentration inside the car can be very highabove 3,000 ppm, and this high concentration of CO₂ may cause headache, sleepiness, and drowsiness. In this study, a feasibility of applying CO₂adsorbent to control indoor CO₂ concentration in car was investigated. A small CO₂ adsorption system was prepared, and installed inside a car.Physical CO₂ adsorbent and chemical adsorbent was loaded in this system, and CO₂ concentration change with and without operation of CO₂adsorption system was monitored. The car was driven in urban area and on highway with 3 passengers. The ventilation mode was varied as freshair intake mode and recirculation mode, and it was found that CO₂ concentration was lower than 1,000 ppm with fresh air intake mode, while itwas higher than 3,000 ppm with recirculation mode. With the operation of CO₂ adsorption system in recirculation mode, CO₂ concentrationcould be lowered to 2,000 ppm within 1 h when chemical CO₂ adsorbent was used. However, when physical CO₂ adsorbent was used CO₂concentration could be lowered much less than the case with chemical CO₂ adsorbent. Physical adsorbent, made of 5A zeolite, was regenerable, butthe efficiency of CO₂ adsorption was lower, and CO₂ capture time was too long. Chemical CO₂ adsorbent, made of metal hydroxide, was nonregenerable,but it could adsorb CO₂ very quickly and efficiently.