A series of blend membranes of poly(phenyl sulfone) (PPSU) with poly(bisphenol A-co-4-nitrophthalic anhydride-co-1,3-phenylenediamine) (PBNPI) were prepared through a solution casting method. This was done to examine the permeation characteristics of oxygen and nitrogen. The effect of the PPSU/PBNPI ratio on the membrane structure and O-2/N-2 separation performance were investigated. The results show that the permeability increased remarkably with the content of PPSU, whereas the selectivity decreased slightly. To enhance the selectivity of O-2/N-2, the blend membranes were further crosslinked with a p-xylylenediamine agent via the immersion method. According to the Fourier transform infrared analysis, the N-H group was formed on the imide group of PBNPI. Therefore, we suggest that during the crosslinking modification, the PBNPI served as a crosslinkable polymer; this resulted in increased crosslinking efficiency with PBNPI content. The high-resolution X-ray diffraction and melting point method results show that crosslinking modification improved the selectivity with an acceptable loss in permeability along with increased crystallinity. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1254-1263, 2010