Among the different chemical compounds used to prevent the aggregation and to control the size of silver nanoparticles, the aminosilanes are interesting because they can simultaneously act as stabilizing and coupling agents. The aim of this study was to investigate the effects of different concentrations of an aminosilane on the synthesis of silver nanoparticles. The functionalized nanoparticles were characterized using UV-vis spectrophotometry, transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and zeta (zeta) potential. Antibacterial assays were also performed. According to the results, increasing the concentration of the aminosilane produced smaller, less dispersed, and more stable silver nanoparticles. Besides the effective antibacterial activity verified in all the concentrations tested, a significant influence on the kinetics of bacteria annihilation was also observed when aminosilane was used in a concentration dependent fashion. These findings indicated the important effects of aminosilane concentrations in controlling the size and stability of the colloids, as well as the rate of silver ions releasing from nanoparticles.