Nitrogen is one of the primary limiting factors for plant growth in the soil and can not be taken up by the trees from the atmesphere directly. Biological nitrogen fixatiorı is the biochernical process to which elemental nitrogen is cornbined into organic forms. It is carried out by a number of organisms and irıcreases the amounts of available nitrogen. It occurs in most, probably all, forest ecosystems, and thus is a factor in all silvicultural systems. Syrnbiotic niırogen fıxation provides the major biological saul'ce of fıxed nitrogen in forest soils. Nitrogen fixing plants as a silvicultural tool have been used increasingly for land reclamation. soil protection. and increasing the amount of humus and available nitrogen content of the soils. Biological nitrogen fıxation and its role in forestry were evaluated in this research.