A novel acrylamide/maleic acid copolymer [P(AM‐MA)] hydrogel nanofibrous membrane with a fiber diameter of ca. 120 nm is prepared by electrospinning an aqueous P(AM‐MA) solution with diethylene glycol as crosslinker, followed by a heat‐induced esterification crosslinking reaction at 145 °C. This hydrogel nanofiber can maintain a fiber form, but becomes distorted and merges to form many physical crosslinking points after immersion in water. The P(AM‐MA) hydrogel nanofibers are sensitive to external stimuli ionic strength and pH. Their water‐swelling ratio decreases with increasing solution ionic strength, and it shows a characteristic two‐step increase at pH = 2.5 and 8.5 in response to the increase of solution pH. The maximum water‐swelling ratios of the P(AM‐MA) hydrogel nanofibers are 18.1 and 22.5 g · g−1 in a solution of 0.05 mol · dm−3 ionic strength and in an aqueous solution of pH 11, respectively.magnified image