Abstract: Acetohydroxyacid synthase (AHAS) is a key enzyme involved in the biosynthesis pathway of branched-chain amino acids, and it is an important target for green herbicides. This enzyme only exists in plants and microbes, therefore its inhibitors are biologically safe to mammals. With the recent elucidation of three dimensional AHAS structures, detailed understanding on the inhibition mechanism of current inhibitors has been achieved, and novel AHAS inhibitors have been designed and discovered. Moreover, AHAS inhibitors have been investigated their new biological function as antimicrobial agents. This review summarizes the progress on AHAS and its inhibitors within recent years, in order to provide useful information for the development of novel herbicides or antibiotics targeting AHAS.