Abstract: Changes in the cell wall components,biomass and calculated ethanol yields (CEY) from cellulose and hemicelluloses of Pennisetum purpureum cv. Sumu No.2 (PP) and hybrid Pennisetum (HP) during 83-173 days after transplanting seedlings (DATS) in Nanjing were studied. With an extension of the growing period,the cellulose (CEL) contents of stems and leaves gradually decreased,but the hemicelluloses (HMC) and the acid detergent lignin (ADL) contents of stems gradually increased in these two species. During the observed growing period,the CEL content of leaves was significantly (P<0.01) higher,while the HMC leaf contents were lower (P<0.01) than those of stems,and the HMC of leaves in PP was higher (P<0.01) than that in HP. During 114-173 days,the CEL content of stems was lower (P<0.05),while the HMC (P<0.01) and ADL (P<0.05) were higher in PP than those in HP. During 83-114 days,the biomass of all cell wall components and the total CEY steadily increased in PP and in HP. There was no significant difference between the two species in CEL and ADL biomass,however,the HMC of stems was much higher than that in leaves (P<0.01). The total CEY and CEY of leaves between the two species were not significantly different,but the CEY of stems was much higher than that of leaves (P<0.01). During 114-173 days,the biomass of all cell wall components and total CEY had been increasing dramatically,and the majority of the increased yields came from the stems. The HMC,ADL and the CEY of leaves had no obvious difference between the two species,but the biomass of CEL and the total CEY in HP was significantly (P<0.01) higher than those in PP.