High purity methane gas from bio-gas has been magnified as an alternative source of energy recently. Gas above 95% purity can be used as fuel for transportation, however only gas above 97% purity can be distributed via pipe lines for domestic usage. Price of 97% purity gas for domestic gas is much higher than 95% purity gas that is used only for transportation, however recovery of methane gas in the process is lower. Purity and recovery of the product is determined by operating procedures. Thus, several researchers are setting their goal to improve profit by controlling operating procedures. Among upgrading processes, the Pressure Swing Adsorption (PSA) is suitable for separation of high purity methane gas in terms of economics. In this study, as step-time in the PSA has huge effect in the entire process, the optimal step-time for maximizing profit is evaluated in the bio-gas upgrading process using PSA. Especially the relation between profit and steptime is taken into consideration. Before optimization, a 4-step PSA model has been built on physics and chemistry theoretical basis. The developed model is also simulated using dynamic simulation software. After that, optimal step-time for maximizing profit is calculated by optimization method.