Nanocomposite biohydrogels comprised of Xanthan gum, Agar, and Gelatin including different weight ratios of Zinc oxide nanoparticles (ZnO−NPs) have been prepared via gamma irradiation technique in presence of methylene bis acrylamide (MBAm) as a crosslinking agent to be employed as antibacterial environmentally benign formulations. The prepared hydrogels were characterized by several techniques: Fourier‐transform infrared spectroscopy for confirming the chemical structure, X‐ray diffraction for crystallographic features and thermal gravimetric analysis for thermal properties. The AFM and SEM were used for investigating the surface features and morphology of the biohydrogels. The results showed that both Gamma irradiation and incorporation of ZnO−NPs improve the gel (wt %) of the prepared biohydrogel nanocomposite from 42.8±1.5 wt% for the unirradiated composite to 81.2±0.9 wt% after exposed to 20 kGy and reaches to 92±0.68 wt% in addition of 0.5×10−2 g of ZnO−NPs. Also, the effect of ZnO−NPs on the antimicrobial activity of the biohydrogel was verified. It was found that the prepared nanocomposite biohydrogels possess good thermal stability and remarkable antimicrobial activity towards different pathogens, thus they can be used in possible biological applications.