Damping-off caused by Rhizoctonia solani J. G. Kühn is a very important plant disease among soil-borne diseases that make severe damages on a wide range of plants in the world. Biological control of this disease with Trichoderma, Gliocladium, Bacillus, Pseudomonas and Rhizobium species has been reported as a successful management method. The results of some researches on this area and the mechanisms of the effect of these antagonistic fungi and bacteria are described here.