The impact of long term application of herbicidal mixtures of 2,4-DEE, butachlor and pretilachlor on soil microbial population were analysed in a permanent herbicidal trial with a rice-rice cropping pattern. The result of the experiment revealed that in the long term herbicide trial, application of mixture of herbicides did not produce any significant changes in the culturable microbial population when compared to the treatment under hand weeding, after nine consecutive crop seasons. The populations of different microorganisms were observed to be more influenced by the organic fertiliser treatments than by herbicide treatments. The integrated nutrient management treatment which had received 75% inorganic and 25 % organics supported higher culturable microbial population and microbial biomass.