The effect of crosslinking on vapor permeation behavior of polyelectrolyte membranes was studied. Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) membranes were crosslinked by using crosslinkers with different lengths between the reactive ends. Crosslinked membranes with a longer crosslinking length showed lower water vapor permeability due to the lower sorption coefficient. It was also shown that the permeation behavior of PAMPS membranes was more affected by sorption than diffusion. For chemical protection applications, the ratio of water over chemical warfare agent permeability (i.e., selectivity) was measured. Due to the high water solubility of polyelectrolytes, crosslinked PAMPS allowed for the selective permeation of water over harmful chemical vapor, showing a selectivity of 20. The addition of electrospun nylon nanofibers in the membranes significantly improved the selectivity to 80, since the embedded nanofibers effectively reduced both diffusion and sorption coefficients of chemical warfare agents.