Abstract: Bacterial antagonists in floating pellet and water-soluble granule formulations, produced using Bacillus megaterium (No.16) with pharmaceutical technology, were tested under both greenhouse and field conditions. When used by broadcasting to rice plants, the floating pellet formulation was as good as a fungicide (Iprodione) in suppressing sheath blight in the pot tests under the greenhouse condition. When sprayed onto rice plants, the water-soluble granule formulation was as effective as a fungicide and was more effective than the floating pellet formulation in the field test when percentage of rice tillers with sheath blight symptoms was assessed.