To obtain a nonwoven fabric which is excellent in the heat resistance and the chemical resistance, of which the fiber diameter is small, and which is excellent in the mechanical strength at a temperature at which it is used; and an electrolyte membrane which is excellent in the dimensional stability when it is swollen by water, and of which an increase in the resistance by a reinforcing material is suppressed.A nonwoven fabric 28 containing fibers 26 of an ethylene/tetrafluoroethylene copolymer having a storage elastic modulus E′ at 25° C. of at least 8×108 Pa and a melt viscosity measured at 300° C. of higher than 60 Pa·s and at most 300 Pa·s, wherein the average fiber diameter of the fibers is from 0.01 to 3 μm; and an electrolyte membrane reinforced by the nonwoven fabric 28.