The extraction of essential oils from Cinnamomum cassia bark and leaf was carried out by hydrodistillation (HD) and microwave-assisted hydrodistillation (MAHD). Chemical compositions of volatile compounds were determined by GC/MS, 1H-NMR and infrared spectroscopy analysis. The dominant constituents found in the essential oils were aromatic compounds (> 90%) including (E)-cinnamaldehyde (CAL) and (E)-cinnamyl acetate (CAC) as the major components. The thermogravimetry (TG) method was used to study thermal stability and volatilization of the oils at room temperature. The bark essential oils exhibited inhibitory effects against a bacterial strain, S. aureus and a yeast strain, S. cerevisiae at MIC value 200 Âµg/mL. The decomposition kinetic of the essential oils was studied via the isoconversional kinetic models using the TG data. Two the isoconversional models, FlynnâWallâOzawa (FWO) and KissingerâAkahiraâSunose (KAS) were used to determine activation energies (Ea) for decomposition of the essential oils.