The chemical composition of the essential oil obtained from dried stem bark of Cinnamomum zeylanicum Blume (Lauraceae) of Delhi region was analyzed by gas liquid chromatography (GLC) and gas chromatography mass spectrometry (GC-MS). The variations in essential oil components under different physical factors have been determined. The volatile components of the stem bark of C.zeylanicum was characterized mainly by cinnamic aldehyde (93.1%) followed by monoterpene l-limonene (3.1%) and sesquiterpenes, viz. 3, 7-guaiadene, cis-calamenene and caryophyllene oxide. Treatment of the oil with alumina enhanced the production of cinnamic aldehyde (97.8%). Except the volatile oil treated with heat and alumina neutral, α-pinene was detected in all the oil samples and its amount varied from 0.2% in normal, sunlight and UV light to 1.1% in silica gel treated oil. l-Limonene was present in all the oil samples and its concentrationmarkedly differed from0.4%in the alumina treated sample to 14.2% in the silica gel treated oil.