White rot fungi can degrade lignin and improve the nutritional value of highly lignified biomass for ruminants. We screened for excellent fungi-biomass combinations by investigating the improvement of digestibility of wheat straw, barley straw, oat straw, rapeseed straw, miscanthus, new reed, spent reed from thatched roofs, and cocoa shells after colonisation by Ceriporiopsis subvermispora (CS), Lentinula edodes (LE), and Pleurotus eryngii (PE) (indicated by increased in vitro gas production [IVGP]). First, growth was evaluated for three fungi on all types of biomass, over a period of 17 days in race tubes. CS grew faster than LE and PE on all types of biomass. LE did not grow on cocoa shells, while growth rate of CS and PE on cocoa shells was lower compared to other types of biomass. After this first screening, all types of biomass, excluding the cocoa shells, were colonised by the three fungal strains for 8 weeks. Treatment with CS and LE improved IVGP more than treatment with PE. Methane production was reduced in six combinations of biomass with CS, four with LE, and three with PE. Six types of biomass were selected for treatment with CS and four were selected for treatment with CS and LE, to determine the net improvement of nutritional value (increased IVGP corrected for dry matter loss) after 2, 4, 6, 7 and 8 weeks of treatment. The highest net improvement was found for CS and LE treated rapeseed straw (86% and 20%, respectively) and spent reed (80% and 43%, respectively). All treatments decreased dry matter, lignin and hemicellulose, the latter two both in absolute amount and content. In conclusion, net improvement of highly lignified biomasses by CS was greater than LE, with the nutritional value of rapeseed straw and spent reed being significantly improved by both fungi.