Abstract: Silver/low molecular weight chitosan(Ag/LMWC) and Ag/LMWC-polypyrrole (PPy) composite colloids were prepared in situ by liquid chemical reduction method.The effects of various process conditions on the size and size distribution of Ag nanoparticles in composite colloids were investigated.And the appropriate synthetic conditions were determined.The component of the composite colloids and the morphological structure of Ag nanoparticles were characterized by UV-Vis, TEM, FTIR and XRD.The results show that the structure of Ag nanoparticles in the composite colloids is face-centered cubic with average particle size about 10-20 nm.The antibacterial tests reveal that the inhibitory of LMWC (viscosity-average molecular weight M_η=4.3×10⁵) is stronger than that of the original chitosan (CS).Moreover, compared with the single LMWC, the antibacterial activities of Ag/LMWC and Ag/LMWC-PPy composite colloids to Escherichia coli and Staphylococcus aureus are very excellent due to the introduction of Ag nanoparticles.