This study was carried out to investigate the effect of yam (Dioscorea opposite) supplement levels on in vitro digestibility, gas production and rumen fermentation characteristics of ground corn and perennial ryegrass using a novel wireless automated gas production system. Rumen fluid was collected from 2 cannulated Hanwoo heifers, filtered by 2 layers of cheese cloth and mixed with Van Soest medium at 1:2 ratio. The rumen fluid mixture (40 mL) added to the incubation bottles containing ground corn or perennial ryegrass (0.5 g) with 4 levels of Yam supplement (0, 5, 25 and 50 mg). Four replicates in each treatment with 2 blanks were incubated at 39°C for 48 h and 72 h for ground corn and perennial ryegrass, respectively. After incubation, the bottle content was used for the analyses of in vitro digestibilities of dry matter (IVDMD) and neutral detergent fiber (IVNDFD), pH, ammonia-N and volatile fatty acid (VFA). Data were analyzed using the GLM procedure of SAS (SAS Inst., Cary, NC). The pH (Linear, P < 0.001) and the concentrations of iso-butyrate (Quadratic, P = 0.025) and iso-valerate (Quadratic, P < 0.001) of ground corn decreased with increasing yam supplementation level, while the concentrations of total VFA (Linear, P = 0.01) and butyrate (Quadratic, P = 0.001) increased. However, the fermentation kinetic of ground corn was not affected by Yam supplementation level. With increasing yam supplementation level, IVDMD (Linear, P < 0.001), IVNDFD (Linear, P = 0.002), the potentially fermentable fraction (Linear, P = 0.057) and the total fermentable fraction (Linear, P = 0.018) of perennial ryegrass increased. Results indicated that yam (Dioscorea opposite) supplementation can increase not only total VFA concentration of ground corn, but also in vitro digestibilities of perennial ryegrass.