As well as cellulose and hemicelluloses, rice straw contains phenolic acids. The simultaneous production of monosaccharides and phenolic acids could improve the value of rice straw. In this study, it was confirmed that Penicillium decumbens produces more ferulic acid esterase (FAE) than other cellulase-producing fungi. Cellulose, destarched wheat bran (DSWB), and rice straw were used as carbon sources. Little phenolic acid was released by cellulose- and DSWB-based enzymes during the saccharification of rice straw, whereas rice straw was a favorable carbon source for the simultaneous production of cellulase and FAE. High-performance liquid chromatography showed that during enzyme production, phenolic acids were released from rice straw, and ball-milling affected this release of phenolic acids. Small amounts of phenolic acids induced FAE production. Although the enzymes produced with rice straw showed lower FAE activity than those produced with DSWB, phenolic acids were produced efficiently during the saccharification of rice straw in response to the synergistic effects of cellulase and FAE. Therefore, we suggest that the production of enzymes by P. decumbens on rice straw as the sole carbon source will allow the production of more valuable products from rice straw, making the utilization of rice straw more economic. (C) 2019, The Society for Biotechnology, Japan. All rights reserved.