This study investigated the effect of particle size on the performance of anaerobic digestion of Hybrid Pennisetum. Hybrid Pennisetum was ground and sieved to provide different particle sizes between 0.180 and 1.000 mm. Characterization of the different particle sizes suggested that the composition of ground Hybrid Pennisetum Wltered-carbohydrate content decreased and lignin content increased with a decrease in particle size. The highest specific methane yield was 291.9 +/- 4.7 mL CH4.g(-1) VS at a particle size of 0.250-0.380mm and this value plateaued as the particle size was reduced to below 0.250 mm. Excessive size reduction did not improve the methane yield but did result in a reduction of digestion time by 28.6-35.7%. The net energy output from the process was calculated at 300 kWh/t VS. Therefore, grinding was proved to enhance the anaerobic fermentation efficiency and energy output of Hybrid Pennisetum.