Abstract: An attempt was made to study the biocontrol activity of Trichoderma atroviride against Phomopsis theae Petch, a causative agent of Phomopsis canker disease in tea plants. Among 78 isolates enumerated, six strains, each representing an agroclimatic zone was chosen for further studies and later it was identified it as Trichoderma atroviride. A range of in vitro assessment such as growth parameters, antagonist activity against P. theae and compatibility with fungicides were evaluated for selected T. atroviride isolates. The correlation of various edaphic and environmental factors with population density of Trichoderma spp. showed positive results. The radial growth measurement and mycelium dry weight of Tv1 isolate obtained from Valparai showed the utmost growth on Potato Dextrose Agar. The highest antagonist activity of 65.77, 91.25 and 69.17% was observed for Tv1 isolates in dual culture test, antibiosis for volatile and non-volatile antifungal compounds. The compatibility of T. atroviride isolates tested against various contact and systematic fungicides clearly showed that Tv1 isolate can able to tolerate the concentration to higher extent. Hence the results revealed that Tv1 isolates proved to be eminent strains in controlling Phomopsis canker disease in tea plants.