Abstract: In order to investigate the resistance of Capsella bursa-pastoris to tribenuron-methyl,13 potential resistant biotypes were collected from 13 winter wheat fields in Shandong,Shanxi,Henan,Hebei,and Shaanxi Provinces,and 13 susceptible biotypes were correspondingly collected from the nearby non-farming lands that never applied herbicides.The resistance level of C.bursa-pastoris to tribenuron-methyl was assessed by three methods:seed bioassay,whole-plant bioassay and acetolactate synthase (ALS) activity in vitro assay.The results of seed bioassay showed that the relative resistance factor of Liangzhu Town in Zhumadian was 6.17,which was the highest.All the other potential resistant biotypes were sensitive to tribenuron-methyl,with a resistance factor ranging from 0.94 to 2.04.The results of whole-plant bioassay showed that the relative resistance factor of biotype from Liangzhu Town in Zhumadian was 233,while those of other potential resistant biotypes were from 1.23 to 3.73.The inhibition of tribenuron-methyl on ALS activity in vitro between the resistant and susceptible biotypes was significantly different,with the IC50 value as 0.664 μmol/L and 0.053 3 μmol/L respectively,and the relative resistance factor to tribenuron-methyl was 12.5.The results indicated that the resistance level of potential resistant biotypes of C.bursa-pastoris from Liangzhu Town in Zhumadian to tribenuron-methyl was higher than that of the others,and decreased sensitivity of ALS may be one of the reasons responsible for the resistance.