Abstract: In order to evaluate the resistance of Lithospermum arvense biotypes to tribenuron-methyl,whole-plant bioassay,seed bioassay experiments and acetolactate synthase (ALS) activity determination were carried out.The results of whole-plant bioassay showed that biotypes of L. arvense from the collecting sites of Shandong Province developed different levels of resistance to tribenuron-methyl,and the highest resistant index(RI) was 12.8,which was found in biotypes from Jiaozhou.The results of seed bioassay experiment also showed that L. arvense biotypes from Jiaozhou have the highest resistance level with RI as 3.89.The results of cross-resistance test showed that L. arvense biotype from Jiaozhou developed resistance to other ALS inhibitor(thifensulfuron-methyl and bensulfuron-methyl), and the RI to thifensulfuron-methyl was 3.11.The IC50 value of tribenuron-methyl against ALS in L. arvense from Jiaozhou was 2.65 times comparing with S biotype in vitro.The results suggested that decreased ALS sensitivity may be one of the main reasons that responsible for the resistance of L. arvense biotypes to tribenuron-methyl.