Formaldehyde and total volatile organic compounds (TVOC) from building materials have been known as main causes of IAQ problem in Newly-Constructed Multi-Family Houses. Because Multi-Family Houses are built in large quantities in a similar manner, inappropriate selection of building materials and method will detrimental affect IAQ. This research aims to identify major causes of Indoor Air Pollutants in Multi-Family Houses, by constructing Mock-Up & One-Room House. As a result, self leveling concrete, door, and furniture construction is a major cause of indoor formaldehyde increase, and tile bond is TVOC, and urethane water proof is Etylbenzene, and Xylene.