Various amounts of cobalt(III) acetylacetonate (Co(acac)(3)) were added to a polycarbonate (PC) membrane to enhance its oxygen enrichment ability. As high as 20 wt% of Co(acac)(3) can be blended with polycarbonate to form a homogenous membrane and a significant improvement of oxygen selectivity was observed, Both the solubility and diffusivity ratio of oxygen to nitrogen increased with the increase of Co(acac)(3) content. But the data indicated that the increase of oxygen/nitrogen selectivity by introducing Co(acac)(3) was mostly due to the increase of diffusivity selectivity of the membrane. The carbonyl functional group of polycarbonate has a distinct absorption at 1780 cm(-1) in the FTIR spectra. This peak splitted after the addition of Co(acac)(3) and the absorbance of the second peak increased with the amount of Co(acac)(3) added. The spilt of the carbonyl peak in the FTIR spectra implied that a specific interaction existed between polycarbonate and Co(acac)(3). It was suspected that the improvement of solubility selectivity was due to this interaction. The O-2/N-2 selectivity measured at 25 degrees C and 1 atm was 8.4 while the flux was 49 (10(-10) cm(3) cm/cm(2) a). The O-2/N-2 selectivity was expected to be higher at a lower operating upstream pressure and the oxygen flux could be increased by operating at a higher temperature.