The effective in vitro screening tests of Trichoderma viride for antagonism against post harvest pathogens of cassava roots (Manihot esculenta Crantz) rot together with its competitive and mycoparasitic abilities informs its selection as the most promising candidate for the biocontrol of post harvest cassava root rot pathogens. While the percentage germination of the spores were observed to increase with increasing dilution of the culture filtrate (100, 50, 25, and 10% ) at a concentration of 20,000 spores/ml, the percentage rot recorded amongst the untreated cassava roots ranged from 4% (Rhizopus oryzae) to 44% (Aspergillus flavus). Treatment with the antagonist and the subsequent storage resulted in a remarkable reduction in the frequency of occurrence of the normal root surface mycoflora and the pathogens over a 3 weeks storage period. Botryodiplodia theobromae and R. oryzae were isolated only in the first week of storage and at a frequency of 3 and 2% rot, respectively, after treatment whereas A. flavus and Fusarium solani persisted throughout the whole storage period with 2 and 3% rot on the third week, respectively. The observed results suggest that T. viride is root surface competent and highly antagonistic.