Abstract: Wheat bran was selected as the substrate from agricultural byproducts for spore production of Bacillus coagulans in Solid State Fermentation (SSF). Its particle size has an obvious influence on spore production in SSF conducted by incubation 60% moisture at 37°C for 48 h. The maximum yield (2.85x1010 cfu g-1) was achieved using the wheat bran particle passed through a 20 mesh sieves without any additional nutrient source to be supplemented.