This study evaluated the indoor air quality in 36 new apartment houses in six big cities in Korea from July 2005 to January 2006. Most of the indoor finishing materials in the new houses were environment-friendly and designated by the Korea Air Cleaning & Researching Association. In the new apartments, which were all built with the same finishing materials, air levels of toluene averaged 1475 μg · m-3 in summer, when there were relatively high temperatures and humidity, and averaged 2711 μg· m-3 in winter. In addition, benzene, ethylbenzene, styrene, xylene, and formaldehyde measured 9.99, 628, 232, 2392 and 951μg·m-3 in summer and 9.99, 628, 232, 2392, and 951μg·m-3 in winter, respectively. Concentrations of volatile organic compounds (VOCs) and formaldehyde were increased as indoor temperature and humidity increased. This study evaluated concentrations of VOCs compounds in a room according to season using enthalpy, which considers two indexes, temperature and humidity. Concentrations of benzene, ethylbenzene, styrene, xylene, and formaldehyde increased with increased enthalpy.