Abstract: In order to provide a scientific evidence for the exploration and usage of Citrus grandis (Linn.)Osbeck,the chemical constituents of its volatile oils was analyzed.The volatile oils of Citrus grandis (Linn.)Osbeck were extracted by Free-solvent Microwave Extraction (SFME) and its chemical constituents were separated and identified by GC-MS.The content of each constituent was determined by area normalization method.59 components were identified in old leaves of Citrus grandis (Linn.)Osbeck,which accounts for 91.29% of the total volatile oils.51 components were identified in young leaves,which constituted about 87.45% of the total volatile oils,and there were significant differences in the leaves.Volatile components in Citrus grandis (Linn.)Osbeck are abundant,and there are lots of aromatic substances and active ingredients,which can be used in the research of essence spice and in the field of traditional Chinese medicine.In addition,oils yield of the old leaves is higher than the young leaves,and its volatile components of old leaves is more than the young ones,therefore the leaves should be harvested at later growth stage.