This study was carried out to evaluate the possible use of plasmodium of a myxomycete as a biological control agent of a cassava (Manihot utilissima) leaf spot disease [brown leaf spot disease] caused by Cercospora henningsii. Cercospora henningsii was isolated from a diseased cassava leaf collected from a cassava farm behind the University of Benin Health Service Centre. The Plasmodium of Didymium alba Ejale (the myxomycete) was cultured from the fructifications collected from the dead twigs of Ficus yoponensis Desdaux tree growing by the building housing the Department of Plant Biology and Biotechnology, University of Benin. The plasmodium of the myxomycete (Didymium alba) was tested in-vitro on the pathogen. During this study, it was observed that the plasmodium of the myxomycete adversely affected the growth of the fungal pathogen. This is a clear indication that the plasmodium of Didymium alba can be used to control Cercospora henningsii –the causal organism of cassava brown leaf spot.