The present study describes synthesis, characterization and antibacterial application of oxidized sodium alginate (OSA)-zinc oxide (ZnO) hybrid nanostructures (OSA-ZnO). In continuation to our previous study on oxidized guar gum (OGG)-ZnO (OGG-ZnO) nanocomposite, in the present study we have chosen OSA to understand the role of polysaccharide charge type in designing the antibacterial material. The nanomaterial has been characterized using UV–visible, FTIR, XRD, SEM and TEM analyses. The nanostructure has shown crystalline nature having hexagonal phase with preferred (101) orientation, while TEM image indicated that the material has ~6 nm particle size. It exhibited very good antibacterial performance against Bacillus subtilis (B. subtilis), Cellulomonas cellulans (C. cellulans), Staphylococcus typhi (S. typhi), and Escherichia coli (E. coli) bacterial strains, ZOI for B. subtilis, C. cellulans, S. typhi, and E. coli being 22, 18, 19.5 and 18.5 mm respectively. Under identical conditions, pure ZnO showed significantly lower ZOI for the corresponding bacterial strains (14, 12.5, 12 and 13.5 mm respectively), while native SA and OSA did not exhibit any biological activity.