Thirteen isolates of Gliocladium spp and four isolates of Aspergillus niger obtained from different sources viz., soil, rice rhizosphere, rice leaves and rice leaf sheath were evaluated for their biocontrol ability against R. solani, the causal agent of sheath blight of rice. Four isolates of Gliocladium spp.(1, 24, 29 and 30) and 4 isolates of Aspergillus niger (35, 36, 37 and 38) were found effective in dual culture. Hyphal interactions between biological control agents and R. solani were observed as hyperparasitic coiling, penetration and finally resulting lysis and collapse of R. solani. Two isolates of Gliocladium spp. (1, 33) and all four isolates of A. niger were found highly inhibitory to the mycelial growth of the pathogen by producing volatile substances. Culture filtrate of the promising isolates of antagonists were also inhibited the growth of the pathogen.