Thermogravimetric analysis (TGA) is a thermal analysis technique that the mass of sample is measured by time and temperature changes. In this study, TGA was applied for estimating the proportion of Nylon-6,6 nanofibers in the cement paste as well as the decomposition temperature of Nylon-6,6 nanofibers. An electrospinning process was conducted for producing nanofibers and adding directly into the cement powder. The TGA results show that there was approximately 0.5 % of nanofibers in the composite pastes. Besides, the decomposition temperature of Nylon-6,6 nanofibers was clarified in the range of 300℃ to 410℃.