Low-humidity sensing performance of generation 1 amine terminated polyamidoamine (PAMAM) dendrimer (G1-NH 2 ), generation 5 amine terminated PAMAM dendrimer (G5-NH 2 ) and G5-NH 2 –Au nanoparticles (G5-NH 2 –AuNPs) thin films were investigated by using a quartz crystal microbalance (QCM). The formation of AuNPs was characterized by UV–vis spectrophotometer. The characterizations of the thin films were analyzed by atomic force microscopy (AFM). Water vapor molecules adsorbed onto the G5-NH 2 –AuNPs thin film had a larger frequency shift than the G1-NH 2 and G5-NH 2 thin films. Adsorption dynamic analysis, molecular mechanics calculation (association constant), was applied to elucidate how number of amine surface functional groups of PAMAM dendrimer and doped AuNPS in PAMAM dendrimer increase the sensitivity to low-humidity.