A pot experiment was conducted to study the toxic effect of nematicides: carbofuran, carbosulfan alone and their combination on soil microbial population and soil respiration with cotton as a test crop. The total bacterial population and free living diazotrophs population was reduced initially by nematicides application. With progress of time after nematicide application, population increased in nematicides treatments in comparison to control. Population of fungi and actinomycetes remained higher in nematicides treated soils till the end of the experiment. Nematicides application resulted in an increase in basal respiration of the soil up to 30 days after treatment (DAT) while at 60 DAT, basal respiration was less in nematicides treatments in comparison to control.