Herbicides being biologically active compounds, an unintended consequence of the application of herbicides is that it may lead to significant changes in the populations of microorganisms and their activities thereby influencing the microbial ecological balance in the soil and affecting the productivity of soils. The increasing reliance of rice cultivation on herbicides has led to concern about their ecotoxicological behaviour in the rice field environment. Hence, in this study, the herbicides viz., 2,4-DEE, butachlor, pretilachlor and pyrazosulfuron ethyl were evaluated at different concentrations of 1 FR (Field rate), 2 FR (two times field rate), 5 FR, 10 FR and 100 FR for their effect on total heterotrophic bacteria, fungi and actinomycetes in laboratory microcosms. The results of this experiment revealed that the application of herbicides reduced the population of all the bacteria counted during the study with butachlor showing highest reduction in the populations. This effect was stronger with increasing concentration of the herbicides employed. However, the populations at 1 FR (and also 2 FR for pyrazosulfuron ethyl) concentrations recovered within 30 days to reach populations not significantly different from the control treatments.