Pomegranate seeds were exposed to electron and gamma irradiations at doses of 5, 10, 15 and 20 kGy to study the relationships between their condensed tannin, NDF, ADF contents, in vitro rumen methane production and protozoa population. Data were analyzed by using the GLM procedure. Orthogonal contrast showed that gamma irradiation significantly increased the NDF content of pomegranate seed as compared to control (P<0.05), however electron beam irradiation did not significantly affect NDF%. The condensed tannin content of the pomegranate seed was significantly decreased by gamma and electron beam irradiation compared to control (P<0.05). Our results showed that there was a negative correlation between the methane production and NDF content of the gamma irradiated pomegranate seed. This means that the methane production of the gamma irradiated pomegranate seed decreased with increasing NDF%. Therefore, it seems that, in addition to tannin, the reduction of the methane production was affected by the cell wall content. Generally, the cell wall content may be more important than tannins in limiting microbial and in vitro fermentation.