Fungal growth in damp or water-damaged building materials is an increasing problem, which has adverse effects on both the occupants and the buildings. Unfortunately, there is still no national standard in Taiwan for evaluating fungal growth on building materials and most of the related studies and methods are not suitable for these. Therefore, this study creates a method for evaluating the degree of fungal growth on building materials. The three moisture indicator fungi（A. niger, P. spinulosum and S. chartarum）were used as test microorganisms. Futhermore, to provide for a more efficient analysis of fungal growth, all the test materials（2 for gypsum board, 1 for calcium silicate board, 3 for cement board and 8 for wood board） were wetted with sterilized water for 1h, and then had their Water Holding Capacity（C_water）calculated. All of the test samples were incubated under controlled conditions（25 °C, 95% RH）for four weeks. The mold growth rate（M_slop）was calculated using the initial mold growth time （M_log）and the mold growth area （M_area）. Finally, we used M_slop, M_area and C_water to analyse the relationship between different building materials and test strains.This study established a semi-empirical model for evaluating the degree of fungal growth on building materials, and has shown to protect indoor environments from mold development effectively.