Abstract: Effects of microorganism and environmental factors on persistence of acetochlor in soils were studied by bioassay using Echinochloa crusgalli. The results indicated that persistence of acetochlor was much shorter in non-sterilized soil than that in sterilized soil under the same conditions of acetochlor concentrations, soil moisture, temperature and light. The period of persistence of acetochlor was shorter in alkaline soil such as cinnamon soil collected from North China than that in acidic soil such as terra nera soil collected from Northeast China and terra rossa soil collected from South China. Within the range of soil moisture and temperature tested, the persistence decreased with increasing of soil moisture or temperature. Longer persistence was observed in light than that in dark. It was considered that microorganism was a key factor and could significantly shorten the persistence of acetochlor in soil, while environmental factors benefiting microbe growth could reduce the persistence of acetochlor. It may be possible to regulate persistence of acetochlor by controlling cultural measures and improving environmental condition.