Nonwoven mats made of a poly(lactic acid)/chitosan (PLA/CS) blend and a PLA/CS blend containing silver (Ag) nanoparticles (Ag/PLA/CS) were prepared using an electrospinning technique. The morphology of electrospun fibers was observed by field emission scanning electron microscopy. The addition of AgNO3 to the PLA/CS blend solution improved the electrospinning ability of the PLA/CS blend. The average diameters of the electrospun PLA/CS and Ag/PLA/CS blend fibers decreased as CS content increased. The Ag particles were evenly distributed in PLA/CS ultrafine fibers observed under transmission electron microscopy. Ag nanoparticles were spontaneously generated during the electrospinning process. When the CS content in the blend increased, the size of the Ag nanoparticles on the surface of the electrospun fibers increased as well. The thermal and mechanical properties of the nonwoven mats were examined by differential scanning calorimetry and a tensile tester. Fourier transform infrared spectroscopy was used to characterize the molecular interactions among PLA, Ag, and CS in the blends. The antibacterial activity of the nonwoven mats against Escherichia coli and Staphylococcus aureus was studied using an optical density method.