AbstractThe importance of utilizing acetolactate synthase (ALS) gene to create herbicide－resistant plant attracted the interest of plant molecular biologists. Understanding the structure , organization , function and the variation of ALS gene in agronomically important species is essential to transfer the resistance. ALS gene was demonstrated to be multigene family among Brassica species. The objectives of this study are (1) to reveal variation of ALS gene among cultivated B . rapa , B . oleracea , and B . napus ; (2) to determine how variation for ALS gene is distributed at the species , subspecies and accessions level ; (3) to evaluate the feasibility of utilizing genetic marker from ALS gene family to discriminate accessions of B . napus. Polymerase chain reaction (PCR) was employed to reach the three objectives. Extensive variation for ALS gene family exists among B rassica subspecies and accessions. The degree of genetic variation differed within different species. At the subspecies level , variation within B . oleracea was lower than that within B . napus , but higher than that within B . rapa. Significant variation was found among accessions of B . napus indicating that the ALS gene family may be used to discriminate among individual accessions.