Poly-gamma-glutamic acid (gamma-PGA) is a natural polymer that is widely recognized as a component in the viscous filaments of fermented soybean (natto). gamma-PGA is known for its superior biodegradability, biocompatibility and water retention characteristics. Crosslinked gamma-PGA is commonly used as a hydrogel, but it is not used in the fiber form because it is soluble in water. In this study, we demonstrate the use of gamma-PGA-Na for production of water insoluble gamma-PGA nanofibers by electrospinning. This result was accomplished using an aqueous solvent containing 10 wt % of an oxazoline component polymer as the crosslinking agent and by heat treatment. The crosslinking reaction was evaluated by solid-state NMR. The nanofiber webs showed a high level of moisture absorption capability while retaining their fibrous shape. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 150-158, 2011