Ensiling of sugarcane trash (SCT) and sugarcane stalks (SCS) was studied to assess the effects of molasses (MOL) and lactic acid bacteria (LAB) inoculant on methane potential. The experiment was run for 70 days and monitoring parameters were analyzed at days 0, 5, 15 and 70. Biochemical methane potential (BMP) tests performed with fresh and ensiled material at day 70 showed an increase in methane potential by 24.0%, 23.4%, 1.7% and 71.1% for SCSctr, SCTctr, SCTmol and SCTmol + lab, respectively. Such improved performance is explained by the formation of organic acids (mostly acetate and lactate) which were able to decrease the pH of the silages from 5.7-5.9 to 3.8-4.2 for all SCT treatments and from 5.9 up to 3.4 for SCS treatment. Thus, the ensiling process provided similar effects to a pre-treatment at low acid concentrations, which in turn improved the digestibility of the cellulosic biomass for methane production.