A 3x2 factorial experimental design was conducted to evaluate the chemical composition ofSesbania grandiflora (SG) and Manihot esculenta Crantz (MEC) leaves and to measure the effects ofpreparation and drying methods on the in vitro gas production in the presence and absence of PEG. Thecollected samples were divided into three groups: One group was fresh samples (F). The second groupwas oven-dried at 55°C for 48h (OD) and the last group was freeze-dried at –40°C for 72h (FD). Resultsshowed that the mean value of gas production from fresh SG and MEC samples were not significantlyhigher (P0.05). Gas production from samples added withPEG were higher (P<0.05) than without PEG. In conclusion, the preparation and drying methods of feedsamples could affect the volume of gas production. The addition of PEG in SG and MEC resulted inhigher gas production volumes