Two in vitro experiments were done to evaluate the green house gas production and organic matter digestibility.  In the first experiment thirteen plant varieties were used for analysis of nutrients and condensed tannin content, then for gas production. The second experiment was a completely randomized design with 5 treatments and 3 replications. The treatments were levels of ground maize at 0, 5, 10, 15 and 20 % (DM) added to the main substrate being Mom grass (Hymenachne acutigluma) corresponding to the GM0, GM5, GM10, GM15 and GM20 treatments. The results showed that in Exp 1, condensed tannin contents were higher than 9.5 % for the P. guajava leaves, mangostine peel and S. samarangense leaves. They gave a lower CH₄ production (less than 0.10 ml/gDOM) compared to others, while Arachis pintoi, P. purpureum and Brachiaria mutica, which were lower in condensed tannin content (less than 2.10 %) and produced higher CH₄ production (more than 8.85 ml/gDOM). In the Exp 2, the total gas, CH₄ and CO₂ production (ml/gOM) at 96 h were significantly (P4 production of the GM15 treatment was significantly higher (Pin vitro CH₄ production, and no reduction of CH₄ effected by increasing supplementation of ground maize to grass was found in the present experiment.