A "post-infiltration and subsequent photo-cross linking layer-by-layer assembly" strategy was, for the first time, introduced to fabricate carboxylated chitosan (CCS) based antibacterial multilayer films with improved stability under alkaline conditions. Precursory polyelectrolyte multilayers were assembled from CCS and poly(allylamine hydrochloride) (PAH). 4,4'-Diazostilbene-2,2'-disulfonic acid disodium salt was then infiltrated to cross-link the multilayers under UV irradiation. Analysis by UV vis spectra showed that absorbance at characteristic wavelengths of the multilayers increased almost linearly with number of CCS/PAH bilayers. AFM images indicated that surfaces of the cross-linked multilayers were rather uniform and stable against basic treatments. Surface wettability of the multilayers was determined by water contact angle measurements. The multilayers exhibited reasonable antibacterial properties against Gram-negative E. coli, demonstrating that the multilayers were active in preventing bacterial growth and represented a novel type of antibacterial films with improved stability under alkaline conditions. These results open new possibilities for building functionalized architectures onto polyelectrolyte multilayer films.