BACKGROUND The capacity of Pleurotus ostreatus to degrade lignin was investigated in the fermentation of cornstalk. Cornstalk was incubated with P. ostreatus for 30 days, and acid-soluble and acid-insoluble lignins were assessed. The microscopic structure of cornstalk samples was studied by scanning electron microscopy ( SEM), and spectroscopic characteristics were measured by X-ray diffraction ( XRD), Fourier transform infrared spectroscopy ( FTIR) and solid state nuclear magnetic resonance ( 13C NMR) spectroscopy. RESULTS During fermentation of cornstalk, the proportion of acid-soluble lignin did not vary significantly ( P > 0.05), but that of acid-insoluble lignin decreased gradually from 17.8% on day 0 to 7.6% on day 30 ( P < 0.01). SEM revealed that the surface of cornstalk was gradually damaged with cavities increasing in number and size, forming a quasi-network structure. Crystallinity decreased from 35.0 on day 0 to 15.2 on day 30. FTIR and cross-polarization magic angle spinning ( CPMAS) 13C NMR spectra showed that the intensity of the peaks corresponding to lignin, cellulose and hemicellulose also decreased gradually over 30 days. CONCLUSION Cornstalk can be effectively degraded by P. ostreatus within 30 days. Pleurotus ostreatus decreases cornstalk lignin content, potentially improving its suitability for animal feed. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]