Silver-dendrimer nanocomposites are synthesized in the presence low generation poly(amido amine) dendrimers with terminal amine groups employing silver nitrate as the precursor and sodium borohydride as the reduction agent. The parameters including the addition of oxalic acid and the generation of the dendrimer that influence the particle size of the synthesized silver nanoparticles are discussed. Under the optimized conditions, a series of silver-dendrimer nanocomposites with the average diameter of silver nanoparticles ranging from 7.6 nm to 16.2 nm are synthesized by varying the molar ratio of dendrimer to silver nitrate. The synthesized silver-dendrimer nanocomposites are utilized as the antibacterial agents in fabrication of antibacterial cotton fabrics. The antimicrobial properties of the prepared antibacterial cotton fabrics against E. coli and S. aureus are evaluated by the inhibition zone method. The results demonstrate that the antimicrobial activity of the silver-dendrimer composites treated cotton fabric enhances with the decrease of the silver nanoparticle size.