Abstract Current work offers two simple synthetic routes for the production of poly-(imidazolium vanillyl)-grafted oligochitosan Schiff bases (PIVCSBs) and their silver nano-biocomposites (NBCs). First, a green in-situ protocol for preparation of silver nanoparticles (AgNPs) using PIVCSBs as a synergetic reductant and capping agent to afford PIVCSBs/Agin NBCs. Contrariwise, in the ex-situ protocol the AgNPs were initially fabricated and then capped by PIVCSBs to fabricate PIVCSBs/Agex NBCs. Structural, morphological and physicochemical features of new architectures were examined by diverse techniques. The obtained NBCs were applied as cotton fabrics antibacterial finishing additives via a pad-dry-curing method. The obtained data revealed that the AgNPs produced by in-situ approach are spherical, smaller size, well-stabilized, and uniformly distrusted when compared with that formed using ex-situ technique as proved by UV–Vis, SEM micrographs and TEM techniques. Moreover, the antibacterial properties of cotton-treated fabrics were evaluated against E. coli and S. aureus species and acquired very strong bactericidal activity to cotton fabrics.