Tetra-PEG gel, which has been known as a mechanically tough and biocompatible gel, was processed into a nanofiber mat by electro-spinning (ES) and 2-step treatment process using w/o type emulsion consisted of the Tetra-PEG prepolymer 1-octanol/water solution. The 2-step treatment was carried out in order to increase the cross-linking points to the as-spun nanofibers. From this study, we succeeded in insolubilizing poly(ethylene glycol) (PEG) nanofiber, and it was found that the Tetra-PEG gel nanofiber mat showed high tensile property even at swollen state. The elastic modulus at equilibrium swollen state was 4.5 kPa. In addition, we compared the differences of the structure and tensile property between the Tetra-PEG nanofiber mat and porous Tetra-PEG gel prepared by freeze-dry method. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41353.