Significance Gas separation by metal-organic framework (MOF) membranes is an emerging research field. Their commercial application potential is, however, still rarely explored due in part to unsatisfied separation characteristics and difficulty in finding suitable applications. Herein, we report sharp molecular sieving properties of high quality isoreticular MOF-1 (IRMOF-1) membrane for CO2 separation from dry, CO2 enriched CO2/CH4, and CO2/N-2 mixtures. The IRMOF-1 membranes exhibit CO2/CH4 and CO2/N-2 separation factors of 328 and 410 with CO2 permeance of 2.55 x 10(-7) and 2.06 x 10(-7) mol m(-2) s(-1) Pa-1 at feed pressure of 505 kPa and 298 K, respectively. High grade CO2 is efficiently produced from the industrial or lower grade CO2 feed gas by this MOF membrane separation process. The demonstrated sharp molecular sieving properties of the MOF membranes and their potential application in production of value-added high purity CO2 should bring new research and development interest in this field. (c) 2016 American Institute of Chemical Engineers AIChE J, 62: 3836-3841, 2016