Abstract: Glasshouse experiments were conducted to evaluate the effect of pre- and post-herbicides on alfala (Medicago sativa) and addition of adjuvants on the performance of imazethapyr. Results indicated that imazethapyr applied pre-emergence at 60-120 g/hm2 resulted in significant injury to alfalfa both on emergence and on seedling growing. When applied in combination with pendimethalin (495 g/hm2), the injury decreased greatly. The safety of post-emergence herbicides closely related with growth stage of alfalfa. Imazethapyr at 120 g/hm2 was excellently safe to alfalfa at 5-leaf stage and seriously damage at 3-leaf stage, and benazolin-ethyl applied post-emergence at 225~450 g/hm2 was safe only after alfalfa 5-leaf stage. Growth of alfalfa was not damaged by addition of nonionic adjuvant PPJ-15, Am-100 or DPS in imazethapyr solution.