The capacities of white rot fungal treatments to degrade lignocellulose and further to improve the rumen degradability were examined in two kinds of corn stover (CAU3138 and ZN01). A total of seven fungi were evaluated according to their growth rates and selective values (SV) on both stovers under 28 °C for 28 days. Then, three selected fungi were evaluated by their in vitro gas production (IVGP) as a measure of rumen fermentation capacity. The results showed that Irpex lacteus, Pleurotus ostreatus, and Pleurotus cystidiosus had high speeds of colonization and high SV on both stovers. The IVGP of the ZN01 treated with any of the three fungi was lower than that of the raw stover, and the IVGP of the CAU3138 treated with P. ostreatus and P. cystidiosus had no significant change (P > 0.05). However, the IVGP of the CAU3138 treated with I. lacteus was significantly increased (P < 0.05) and further increased as the treatment time was prolonged. This study indicated that SV was not always a good predictor for the performance of the fungus. Here, I. lacteus performed best, regarding fungal growth and IVGP of the CAU3138.