A series of activated carbons were prepared by H3PO4-mechanical force activation and characterized by N-2 adsorption/desorption isotherms, SEM, FTIR, CO/CO2-TPD, and XPS. Adsorption isotherms of CH4 and N-2 were measured in the range of 25-760 mmHg at 20 degrees C and fitted by Langmuir model to calculate separation coefficient of CH4 against N-2 (alpha(CH4/N2)). Results showed that H3PO4-mechanical force activation had significantly enhanced the micropore volume of activated carbons (ACs), in which the highest micropore volume (0.8 cm3/g) and BET specific area (1966 m2/g) were obtained under the optimum condition of phosphoric acid impregnation ratio of 1:1, activation temperature of 400 degrees C, and activation time of 60 min. The micropore volume and surface properties of ACs affected its selectivity adsorption ability toward CH4. The ACs with higher micropore volume had a larger adsorption amount of CH4. And the larger the O/C ratio of the ACs was, the larger the oxygen-containing groups on the ACs would be, which can improve the surface polarity of ACs and enhance the adsorption ability of N-2 with certain polarity, and thus make the ACs having the smaller separation factor of alpha(CH4/N2). Among all of the samples, AC-1-400 with the largest micropore volume and O/C ratio had the highest CH4 adsorption amount but the smallest alpha(CH4/N2).