Display omitted •Synthetic routes of poly-(imidazolium vanillyl) chitosan Schiff bases (PIVCSBs) are reported.•Two protocols have addressed for preparation of AgNPs, green and chemical.•AgNPs-based NBCs have been fabricated via capping of AgNPs with PIVCSBs.•Applying of NBCs to cotton fabrics acquired them potent antimicrobial efficacies.•Treated cotton fabrics have strong bactericidal activity. 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.