Separation of light hydrocarbons (C1-C3) is extremely significant since these are alternative energy resources and raw materials in the industrial process. In this work, we have examined the performance of S-graphite slit pore in selective separation of CH4 over C2H2, C2H4, C2H6, C3H6 and C3H8 using Grand Canonical Monte Carlo calculations. Generally, its C3/C1 selectivity is higher than C2/C1 selectivity. Exactly, at 300 K and 1 bar, the selectivity is around 13, 17 and 18 for CH4/C2H2, CH4/C2H4 and CH4/C2H6 while it is about 63 and 70 for CH4/C3H6 and CH4/C3H8, respectively. Importantly, we have found that the optimum pore size is 0.65 nm for CH4/C2H2 and CH4/C2H4, 0.75 nm for CH4/C2H6, which is smaller than that (1.0 nm) for CH4/C3H6 and CH4/C3H8. Besides, density functional theory calculations demonstrate the remarkable selective separation of CH4 over C2H2, C2H4, C2H6, C3H6 and C3H8 of S-graphite slit pore is attributed to its stronger interactions with C2H2, C2H4, C2H6, C3H6 and C3H8 molecule than CH4 molecule due to the larger polarizability of C2 and C3 molecules, which also manifests that S-graphite slit pore is an extremely promising candidate for separating light hydrocarbons. (C) 2018 Elsevier B.V. All rights reserved.