NOVELTY - Method of processing wastewater, involves (a) adding culture solution (S1) (0.1 volume/volume%) to wastewater composition (C1), and reducing biological oxygen demand (BOD) in wastewater, or (b) adding culture solution (S2) (0.1 volume/volume%) to wastewater composition (C2), and reducing BOD in wastewater.    USE - The method is useful for processing wastewater from factory and office.    ADVANTAGE - The method is simple, stable, cost-effective and performed effectively even if wastewater temperature fluctuation is high, avoids need of large-sized installation of apparatus, and prevents water pollution caused by discharge of wastewater into river.    DETAILED DESCRIPTION - Method of processing wastewater, involves (a) adding culture solution (S1) (0.1 volume/volume%) to wastewater composition (C1), and reducing biological oxygen demand (BOD) in wastewater, or (b) adding culture solution (S2) (0.1 volume/volume%) to wastewater composition (C2), and reducing BOD in wastewater. The culture solution (S1) is obtained by culturing mixture of 2 or more types of microorganisms belonging to Bacillus in trypto soy culture medium (having pH of 7) at 10-15 degrees C. The culture solution (S2) is obtained by culturing equivalent mixtures of microorganisms belonging to Bacillus in Trypto soy culture medium. The BOD decreasing rate in the wastewater composition (C1) after 48 hours of cultivation is 50% or more at 25 degrees C. The BOD decreasing rate in the wastewater composition (C2) after 48 hours of cultivation is 50% or more at 15 degrees C. The wastewater composition (C1) comprises (in g/l): soluble starch (0.092), peptone (0.196), yeast extract (0.196), meat extract (0.224), sodium chloride (0.020), magnesium sulfate heptahydrate (0.012), potassium dihydrogen phosphate (0.056), potassium chloride (0.040), and ammonium chloride (0.060), and has BOD value of 600 mg/l. The wastewater composition (C2) comprises (in g/l): glucose (0.60), collagen peptide (1.20), yeast extract (0.60), pork bouillon (0.60), sodium chloride (0.10), magnesium sulfate heptahydrate (0.28), potassium dihydrogen phosphate (0.20), potassium chloride (0.06) and ammonium chloride (0.30), and has BOD value of 2000 mg/l. An INDEPENDENT CLAIM is included for microorganisms belonging to Bacillus for performing the above-mentioned method.