Isobaric vapor liquid equilibrium (VLE) for the binary system N, N-dimethyl formamide (DMF) + N, N-dimethyl acetamide (DMAC) and the quaternary system sec-butyl alcohol (SBA) + sec-butyl acetate (SBAC) DMF DMAC were determined at 101.3 kPa using a vapor liquid equilibrium still. The thermodynamic consistency test for the experimental data was checked by Van Ness point test. The binary VLE data were correlated with the NRTL, UNIQUAC and Wilson activity coefficient models respectively. And the VLE data of the quaternary system predicted by the correlated binary interaction parameters agree well with the experimental data. And the mixture of DMF (3) and DMAC (4) can eliminate the pseudo-azeotrope of sec-butyl alcohol (1) + sec-butyl acetate (2). Thus, the mixture of DMF and DMAC is appropriate for separation of the pseudo-azotrope of SBA and SBAC by extractive distillation. (C) 2015 Published by Elsevier B.V.