Diacetyl, a highly valuable product that is extensively used as an ingredient of food, tobacco, and daily chemicals such as perfumes, can be produced from the nonenzymatic oxidative decarboxylation of alpha-acetolactate during bacterial fermentation and converted to acetoin and 2,3-butanediol by 2,3-butanediol dehydrogenase. In the present study, Bacillus sp. DL01, which gives high acetoin production, was metabolically engineered to improve diacetyl production. After the deletion of alpha-acetolactate decarboxylase (ALDC)-encoding gene (alsD) by homologous recombination, the engineered strain, named Bacillus sp. DL01-Delta alsD, lost ALDC activity and produced 1.53 g/L diacetyl without acetoin and 2,3-butanediol accumulation. The channeling of carbon flux into diacetyl biosynthetic pathway was amplified by an overexpressed alpha-acetolactate synthase (ALS)-encoding gene (alsS) in Bacillus sp. DL01-Delta alsD-alsS, which produced 4.02 g/L alpha-acetolactate and 1.94 g/L diacetyl, and the conversion from alpha-acetolactate to diacetyl was increased by 1-fold after 20 mM Fe3+ was added to the fermentation medium. A titer of 8.69 g/L diacetyl, the highest reported diacetyl production, was achieved by fed-batch fermentation in optimal conditions using the metabolically engineered strain of Bacillus sp. DL01-Delta alsD-alsS. These results are of great importance as a new method for the efficient production of diacetyl by food safe bacteria.