Objective: To investigate the antimicrobial activities of various solvent extracts of the bark of Cinnamomum cassia and Cinnamomum zeylanicum. Methods: The powdered barks of C. cassia and C. zeylanicum were extracted using methanol, ethanol and acetone. The antimicrobial activity of methanolic, ethanolic and acetone extracts of barks of C. cassia and C. zeylanicum were studied using agar well diffusion method against seven ATCC bacterial species (Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, Streptococcus pyogenes, Escherichia coli, Salmonella bongori and Pseudomonas aeruginosa). The antimicrobial activity of extracts of C. cassia and C. zeylanicum were compared with gentamycin. Results: The ethanolic and acetone extract of C. cassia and C. zeylanicum showed greater zones of inhibition than methanolic extract. C. zeylanicum inhibited the growth of all seven ATCC strains used in this study whereas, C. cassia inhibited the growth of S. pyogenes, S. aureus, B. cereus, E. faecalis, P. aeruginosa and S. bongori. Gentamycin inhibited the pathogenic group of all ATCC strains used in this study. Conclusion: The ethanolic and acetone extracts of bark of C. Cassia and C. zeylanicum exhibited a broad spectrum of exhibited a broad-spectrum antimicrobial activity.