In the present study the effectiveness of Cleistanthus collinus on inactivation of some microorganisms i.e. Pseudomonas fluorescens, Xanthomonas auxinopodis, Rhizoctonia bataticola, Fusarium udum were determined. The agar well diffusion method was used for screening of crude methanolic extract of leaf and bark for antimicrobial activity. The methanolic extract presented antimicrobial activity against all the four microorganisms. Methanolic leaf extract presented the largest inhibition zones (25.66 mm) against Xanthomonas auxinopodis. The MIC of the methanolic leaf extract was between 1 to 0.1 ?g/ml while that of methanolic bark extract was 0.1?g/ml. When leaf and bark extract were partially purified using solvent extraction procedure, chloroform fraction of leaf extract was found to have better antimicrobial activity. The ability of C. collinus extracts to inhibit the growth of bacteria and fungi is an indication of its broad spectrum antimicrobial potential which may be employed in the management of microbial infections.