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-AAA) solution with diethylene glycol as crosslinker, followed by a heat-induced esterification crosslinking reaction at 145 degrees 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.