The cation-exchange resin-mixed polyethersulfone (PES)-based fibrous adsorbents were developed to study their adsorption behavior with bovine serum albumin (BSA). A fibrous adsorbent with an open pore surface had much better adsorption behavior with a higher adsorbing rate. The adsorption capacity of the Lewatit CNP80ws resin or SP112ws mixed PES-based fibrous adsorbents with an open pore surface was in the range of 68.2–93.2 mg BSA/g adsorbent for 50% resin loading, which was comparable with the resin static adsorption capacity. Compared to a thick fibrous adsorbent, a fibrous adsorbent with a thin diameter had the higher adsorption capacity with BSA. The results showed that the adsorption for cation-exchange resin-mixed PES-based fibrous adsorbents were controlled by a diffusion process whether in matrix pores of the adsorbent or that of resins.