Airborne molecular contaminants in indoor or cleanroom air have been recognized as the important problems of human health or semiconductor processes. It was reported that the emission flux of volatile organic compounds (VOC) was controlled by the evaporation from building material surfaces and the internal diffusion within the building materials, therefore the internal behavior is the important factor for understanding the emission mechanisms. In this study, the VOC emission from the surface and the concentration of VOC within the building material were evaluated by using the small environmental chamber methods under different temperatures and using the screening test method, respectively. Then the model with the factor of VOC diffusion in the materials and the mass transfer from the material surfaces was used for estimating the emission flux from the experimental internal concentration data within the material. As a result, the emission flux that could be extrapolated by the model agreed with the chamber test data therefore it was clarified that the internal concentration within the material had a great effect on the emission flux.