The aim of the experiment was to evaluate the CH4 and CO2 production and organic matter digestibility (OMD) by replacing Para grass to rice straw as the main substrate. This experiment was arranged in a complete randomized design in vitro condition with 5 treatments and 3 replicates by using the glass syringe system. The treatments included 100% rice straw (PG0), 75% rice straw + 25% Para grass (PG25), 50% rice straw + 50% Para grass (PG50), 25% rice straw + 75% Para grass (PG75) and 100% Para grass (PG100) based on DM basis. The results indicated that in vitro CH4 and CO2 production (ml/g DOM) at 72 h were significantly different (Prelationship between CH4 production (ml/gDOM) and Para grass replacement to rice straw was closed with the function y = 0.306x +34.1 (R2 = 0,972). Similarly, the OM digestibility significantly different (Ptreatments and was 42.0, 49.8, 56.8, 63.9 and 79.9% for the PG0, PG25, PG50, PG75 and PG100 treatment, respectively. It was concluded that there was an increase of in vitro GHG production and OMD when increasing the replacement levels of Para grass to rice straw, and the nitogen-free extract (NFE) had a possitiverelationto the methane production. Keywords: degradation, fermentation, local feed sources, roughages, ruminants.