Itaconic acid is commercially produced by the cultivation of Aspergillus terreus using starch hydrolysate as carbon source. The degree of hydrolysis had a great influence on itaconic acid production which was suitable when corn starch was saccharified at 35 DE. The α-amylase was sufficient to drive the starch hydrolysis to the degree. The agar plate assay with LiCl treatment provided a rapid, simple and unequivocal method for screening large numbers of colonies for itaconic acid producing strains. It was learned by experience that the strains on the plates with thick hyphae and light-colored spores often accompanied high itaconic acid production. A strain, designated Ast165, producing itaconic acid with a high yield, was successfully obtained by directional breeding of metabolic end products resistant strains. The itaconic acid concentration produced by Ast165 was 53.8 g/l from 100 g/l of starch hydrolysate in shake flasks. The conversion rate was 61.3%, which was the highest value found in tests.