A more soluble polyaniline derivative, i.e. poly(o-anisidine), (POAn), was synthesized in-house for this study by using an ortho substituted aniline monomer. It was observed that the prepared dope solution was more homogeneous with less visible agglomerates as compared to previously prepared polyaniline (PAni) solution. Integrally skinned hollow fibre membranes were successfully prepared by dry-jet wet spinning from POAn with N-methyl-2-pyrrolidone as a solvent and a more volatile tetrahydrofuran as a co-solvent for gas separation. The spinning air-gap lengths were varied to promote the formation of the membrane skin layer. POAn membranes prepared at higher air gap were more orientated with packed structure and good gas separation characteristics. They showed selectivities of O-2/N-2, CO2/N-2, H-2/N-2 and H-2/CO2 of about 13, 89, 370 and 4.2, respectively with permeation rates of H-2, CO2 and O-2 about 10.4, 2.5 and 0.37 x 10(-6) cm(3) (STP)/cm(2) s cmHg, respectively. Presence of methoxy group in POAn showed substantial enhancement in gas permeation properties compared to previously developed PAni membranes. The H-2/N-2 and CO2/N-2 selectivities were improved by 3 and 7 times, respectively as compared to PAni membranes. Development of hollow fibre membranes using polyaniline derivative with improved processability and excellent gas separation performance depicts their potential for industrial gas separation applications. (C) 2012 Elsevier B.V. All rights reserved.