Abstract: The 0.28 nm resolution crystal structure of yeast acetolactate synthase in complex with a sulfonylurea herbicide,chlorimuron ethyl and the 3D structure of Arabidopsis thaliana acetolactate synthase in complex with sulfonylureas and imidazolinone herbicides were reviewed. Neither class of these molecules has a structure that may mimic the substrates for the enzyme,they act by blocking a channel of the ALS through which access to the active site.Ten of the amino acid residues that bind the sulfonylureas can also bind with imazaquin (IQ).Six additional residues interact only with the sulfonylureas,whereas there were two residues that bind IQ but not the sulfonylureas.The mutation of ALS residue sites causes the appearance of resistant weed,and it also changes the binding mode between herbicide and ALS.Research advances on the 3D structure of ALS is important to discover molecular mechanism of mutation of the weed and for the rational design of further herbicidal compounds.