The aim of this study is to compare the antibacterial activities of various parts (barks, buds and leaves) of Cinnamomum cassia extracted with ethanol and supercritical fluid extraction (SFE). The results obtained from the disk diffusion method and minimum inhibitory concentration (MIC) demonstrated that the SFE extracts of buds displayed significant antibacterial activity against the drug resistance pathogens, with MIC range between 0.3 and 0.7 mg/mL. Following the spectrophotometer analysis, (E)-cinnamaldehyde, O-methoxycinnamaldehyde, coumarin and eucalyptol were evidenced to be the major antimicrobial components in the SFE extracts. The antimicrobial mechanism was also investigated. The results suggested that the active components possess bactericide activity and interact on the cell membranes. In conclusion, the SFE extracts of buds have the potential value as an antibiotic substitute based on the in vitro antimicrobial assay. In addition, this study also provides a best SFE extraction condition to obtain high purity and yield of bioactive substances from C. cassia.