Rhizobium is a biofertilizer for leguminous crops. To formulate this form of fertilizer, the suitable sterilization processes of carrier are important. Therefore, the aim of this research was to elucidate the process of gamma irradiation and autoclaving on peat and compost based carriers for rhizobial inoculant production. Carriers with 10% moisture content packing in polyethylene bag could be efficiently sterilized by irradiation at 10-20 kGy, or by autoclaving with tyndallization approach (autoclaving two times in a row at 121ºC for 60 min, with waiting period of 18 hours after each time of autoclaving). The number of Bradyrhizobium sp. PRC008 was in the range of 10 8 -10 9 cfu/g in both irradiated and autoclaved peat after 6 months storage. However, the numbers of bradyrhizobial cell were reduced in compost sterilized by both methods after one month storage. These results indicated that carrier material had an important influence on inoculant quality, while sterilization processes using gamma irradiation and autoclaving with tyndallization approach could be used for efficient rhizobial inoculant production with peat based carrier.