Poly-gamma-glutamic acid (gamma-PGA) is a natural polymer that is commonly found in the viscous filaments of fermented soybean (natto). gamma-PGA is known for its superior biodegradability, biocompatibility, water retention, and ability to adsorb metal ions. We used an oxazoline-containing polymer (OXA) as a cross-linking agent and succeeded in preparing gamma-PGA nanofibers by electrospinning with a water solvent system. The non-woven gamma-PGA/OXA sheet (90/10 wt%) was treated with alum to improve both the mechanical and antibacterial properties by metal adsorption. The absorption of water for the alum-treated gamma-PGA/OXA non-woven sheets decreased by half compared to the untreated sheets. The tensile modulus did not decrease, and the strength largely improved, even if the webs absorbed moisture. The webs endured high-pressure steam sterilization and exhibited antibacterial properties.