The goals of this study are to compare differential gene expressions for Penicillium oxalicum wild type strain (WT), mtr23B knockout strain (?mtr23B) and complemented strain (Rmtr23B) on Vogel’s medium with 2% glucose (G) or 1% wheat bran and 1% cellulose (CW) as carbon resources. When cultivated in a repression medium for cellulolytic enzyme formation (G), the deletion of mtr23B upregulated genes involved in lyase activity, hydrolase activity, acyl carrier activity, monooxygenase activity, electron transfer activity, phosphopantetheine binding, heme binding, cell wall organization or biogenesis, oxidation-reduction process and extracellular region. The downregulated genes in ?mtr23B were mainly involved in transmembrane transporter activity, amino acid transmembrane transporter activity, membrane and integral component of membrane. When cultivated in an inducing medium for cellulolytic enzyme formation (CW), the downregulated genes in ?mtr23B were mainly involved in glucosidase activity, polygalacturonase activity, oxidoreductase activity, heme binding, oxidareductase activity, xylanase activity, cellulase activity, cellulose binding, oxidation-reduction process, cellulose catabolic process, xylan catabolic process and extracellular region. We find the expression levels of five secondary metabolism gene clusters (totally 28 clusters) were silenced in ?mtr23B. This study provides the information that mtr23B is required in conidiation and hydrolase activity of P. oxalicum. Overall design: Examination of differential gene expressions by digital gene expression tag profiling in Penicillium oxalicum wild type strain and two mutant strains. qRT–PCR validation was performed using SYBR Green assays.