Flavour is an important characteristic of traditional Chinese medicine (TCM) raw materials. For the purpose of genus identification and quality control, flavor of TCM raw materials also act the crucial roles. Essential oils are the major source of the flavour of TCM raw materials. Because of the chemical properties of essential oils, high performance liquid chromatography (HPLC) is not suitable to perform the most quantitative analysis rapidly and accurately. It is popular to use gas chromatography (GC) coupled with different detector to analyze such kinds of essential oils, while the GC coupled with the mass detectors (GC/MS) is the most powerful instrument to perform the analysis of essential oils. In the qualitative analysis, GC/MS data from the test samples could provide the most possible structure by comparing the m/z scale using the related GC/MS database. In the quantitative analysis, concentration of essential oils in TCM raw materials can be analyzed and determined through the information of calibration curve. Sun Ten Pharmarceuticals has already performed several kinds of essentials oil extractions followed by Taiwan Herbal Pharmacopoeia and established the essential oils library of TCM raw materials, such as ginger oil, clove oil, lavender oil, rosa oil, tea tree oil and cypress oils. The GC/MS analysis system can be applied for the essential oils analysis of TCM raw materials and TCM products. These analysis results can be summarized to establish the essential oil database which would be useful for the quality control of the complicate TCM raw materials.