Abstract: 【OBJECTIVE】Sensitivity of rice seeding and antidotal effect on imazethapyr from a new type of biological reagent were studied 【METHOD】by a room bioassay. And the root length and the fresh weight of roots of rice were as biological parameter.【RESULTS AND CONCLUSION】The experiment results show that imazethapyr could significantly suppress the growth of rice seeding and the antidotal effect of biological reagent is good. The protected rate of the reagent was an increasing trend by increased dose of biological reagent, but the increased range was tended to be balanced. The maximum protected rate of biological reagent to rice seeding from imazethapyr injury on root length and root fresh weight were 132 % and 158 % respectively. The optimum economic dose of biological reagent was 30~60 kg/hm2.