Abstract: Germinating seeds of three rice varieties (a high quality HuaXianZhan, a hybrid YueYouQingZhan and a common SuiLingZhan ) were treated with acetochlor at different concentrations. The growth of rice seedling was differently inhibited. HuaXianZhan was the most sensitive variety, SuiLingZhan the most resistant and YueYouQingZhan the intermediate. There was a respiratory peak found on 4-6 days after germination for all the three varieties. For sensitive variety, acetochlor showed a heavy inhibition to respiratory rate, especially, to respiratory peak, which was strengthened by EMP and PP pathways, and eventually, the seedling growth was inhibited greatly. However, the resistant one was affected only slightly in both respiratory rate and respiratory peak, therefore, its seedling growth was subjected to just a little inhibition.We concluded that these could be one elementary physiologcial cause for the growth inhibition of sensitive rice seedlins by acetochlor.