Abstract An investigation was carried out to estimate soil respiration rate and its relationship with microbial population in natural tropical forest soil, deforested soil and deforested-and-cultivated soil of Orissa, India. Soil respiration measurements and microbial isolation were performed following standard procedures. Monthly variation of soil respiration was observed to be governed by soil moisture. Considering respiration as a function of microbial population a regression analysis was made. The microfungal population showed positive relationship with the rate of soil respiration. The study revealed that conversion of natural forest led to a reduction of soil microbes and rate of soil respiration. Considering the importance of the microbial component in soil, we conclude that the conversion of natural forests to different land uses leads to the loss of biological stability of the soil.