This study is involved in developing an I.A.Q. monitoring system that regularly measures air quality inside Cheongok cave at investigating effects of the numbers of tourists on the cave`s air quality. The results indicate that the outside temperature of the cave had a stronger effect on the temperature and humidity of Cheongok cave than the number of tourists. The range of variations was significantly wider than ones investigated in other caves. With regard to carbon dioxide concentration, it has been found that the degree of carbon dioxide concentration was highly influenced by the number of tourists, which is contingent on seasons, and the maximum value of concentration was higher than 3,000ppm. In addition, green pollution that is caused by lighting fixtures inside the cave and other pollution caused by tourists were observed. More detailed and qualitative monitoring and analyses are needed to conserve the environment of Cheongok cave and to provide tourists with pleasant visiting experiences.