Groundnut (Arachis hypogaea L.) is an important oil seed crop. A large number of diseases attack on groundnut such as root rot, Stem rot, crown rot, pod rot, charcoal rot, black rot etc. These diseases cause the serious damage to this crop. In present investigation an attempt has been made to evaluate the In vitro antagonistic activity of Trichoderma harzianum against soilborne pathogens of groundnut like Aspergillus flavus, Aspergillus niger, Fusarium roseum, Macrophomina phaseolina, Phythium myriotylum, Rhizoctonia solani, and Sclerotium rolfsii. The results indicate that the application of Trichoderma harzianum reduces the growth of soilborne fungal pathogens as compared to control. The maximum inhibition was revealed against Fusarium roseum (62.18%), followed by Phythium myriotylum (51.85%), Aspergillus flavus (50.37%), Aspergillus niger (46.55%), Rhizoctonia solani (41.78%), Macrophomina phaseolina (30.58%) and minimum inhibition was shown against Sclerotium rolfsii (27.73%).