The aim of this study was to evaluate the effects of fungal treatment on chemical composition, lignin composition and in vitro rumen degradability of lower parts of corn stem (LCS, internodes 6 and 7). Two lignin degrading fungal species (Lentinula edodes and Pleurotus eryngii) and 2 corn cultivars (LG30211 and MZP8057), which differed in lignin content and rumen degradability were used. Autoclaved LCS was inoculated at 24°C and a relative humidity of 70% in an air-conditioned chamber for 3, 6, and 9 wk and autoclaved LCS was used as control. All treatments were tested in triplicate. Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) content were determined. Lignin composition was analyzed by pyrolysis GC-MS and S:G ratio (ratio of syringyl units to guaiacyl units being lignin building blocks) was determined. An in vitro gas production (IVGP) technique was used as a measure of rate and extent of organic matter degradability (OMD). Data on chemical composition, S:G ratio, and IVGP were analyzed using a generalized linear model in SAS (v9.3) with corn cultivar, fungal species, and inoculation time as fixed effects as well as their interactions. Compared with untreated LCS, incubation with fungi increased NDF, ADF, and ADL content and S:G ratio of LCS significantly (P < 0.05) for both corn cultivars. Only numerical differences of NDF, ADF, and ADL content and S:G ratio were found among LCS treated with fungi for 3, 6, and 9 wk. IVGP within 72 h, which represents OMD, was 263 mL/g OM in control LCS, decreased to the lowest value (178 mL/g OM) after 3 weeks treatment with fungi (P < 0.05) and slightly increased (203 mL/g OM) afterward. In conclusion, treatment of LCS with L. edodes and P. eryngii did not improve rumen degradability of LCS within 9 weeks treatment.