Soil organic matter (SOM) is composed of microorganisms, fresh residues and humus fractions. Measurement of soil microbial activity, in conjunction with other soil physical and chemical properties and processes, can be a valuable tool for developing a complete profile for soil fertility and may be used to increase the efficiency of fertilizer recommendations. Soil microorganisms are the centerpiece of biogeochemical cycling of nutrients in soil. Soil fertility is directly related to, and defined by, the heterotrophic activity of soil microbes as a whole. The breakdown of added residues and of SOM is affected by their physical and chemical characteristics, as well as by temperature, moisture, nutrition, and other factors that affect biological activity directly. Investigation about soil organic matter is continues by researchers and this review indicated the positive effects of soil organic matters on soil structure, soil porous, and soil electro conductivity, microorganisms, carbon and nitrogen rate. Knowledge about soil microorganisms and soil biological processes may improve the scientific basis of management decisions, e.g., determination of the type of species to be used for planting and cropping in agricultural areas.