[Objective] This paper aimed to explore the influences of common herbicides and its concentration on soil microbial populations and enzyme activities in order to provide a reference basis for evaluating its soil ecology effect in paddy field. [Methods] A paddy field experiment treated with low

medium and high concentrations of two herbicides was conducted. The two herbicides were sensulfuron-methyl+scetochlor

W.P and butachlor. [Results] (1) Herbicides with low or medium concentration had little effects on the numbers of microorganisms. Though short term inhibition existed

microorganisms can recovered quickly; (2) High concentration of herbicides had obvious inhibition

it can last about 20 days

and after that

the numbers of microbe recovered to the control background level; (3) These two herbicides had inhibition effects both on soil urease and invertase to a certain extent

and this inhibition was enhanced when concentration increased. As time went on

the inhibition effect declined gradually

and the activity returned to the control level; (4) The two herbicides showed a certain stimulation to catalase activity

this is different from that on soil urease and invertase. [Conclusion] The effects of the two herbicides on soil microbial populations and enzyme activities varied with concentrations and the lasting time after application. The low and medium concentrations had little impacts on either microbial numbers or enzyme activities

and they can recover to the control level in a short term. Therefore

medium concentration of herbicide or low was relatively safe for soil ecosystem in paddy field.