The aim of this study was to use a modified bioreactor system for simultaneous saccharification of cellulose and bioethanol production. We tested Aspergillus niger and Trichoderma reesei for cellulose saccharification and Zymomonas mobilis for bioethanol production simultaneously in this modified bioreactor. The results showed that various carboxymethylcellulose (CMC) concentrations (10,15, or 20 g/L) as a substrate for A. niger and T. reesei yielded bioethanol production of 0.51, 0.78, and 0.89 g/L and a CMC conversion rate of 10.2%, 10.7%, and 8.89%, respectively. These data suggested that at 10 g/L CMC as a substrate, the CMC conversion rate was higher than that at the other concentrations. When CMC concentration exceeded 15 g/L, bioethanol production was prolonged to 40 h. These results were attributed to the viscosity of CMC. This study also tested Napier grass (an agricultural byproduct) for bioethanol production. The results revealed bioethanol production and the theoretical Napier grass conversion rate were 0.38 g/L and 12.6%, respectively, for 13-h cultivation when the feeding concentration of Napier grass was 10 g/L. When Napier grass concentration was increased to 15 g/L, bioethanol production and the Napier grass conversion rate reached 0.51 g/L and 23%, respectively, after 14-h cultivation. Eventually, the experimental results indicated using agricultural waste for bioethanol production has been become a potential strategy. (C) 2017, The Society for Biotechnology, Japan. All rights reserved.