In this stuty, overexpression of the ilvBN gene, enconding acetohydroxy acid synthase (AHAS), in the valine-prouducing strain Brevibacterium flavum XVO5O5 resulted in increased valine production by 9.85% and decreased alanine and acetic acid (the main by-products) by 30.49% and 20.89%, respectively. Metabolic flux analysis revealed a 19.9 % increase of valine synthase pathway in response to overexpression of the ilvBN. The benefit of overexpressing ilvBN was that it resulted in an intracellular pyruavte concentration decresed from 10.45mM to 4.42mM, which means that more carbon flux entering efficiently the pathway of synthesizing L-valine. It could be concluded from the results that ilvBN overexpression was essential achieve suffient carbon flux towards the desired product. Overexpression of ilvBN reduced pyruvate availability for L-alanine formation and therefor resulted in L-alanine reduction.