In order to identify the ingredient in Melaleuca alternifolia oil cells at room temperature, and avoid sample pretreatment and extractions, which can be labour-intensive. Oil Cells Distribution on Different Parts of Melaleuca alternifolia and the principal component in oil cells have been studied by Micro-Raman Spectrometer. It has been found that there are barely any oil cells on the soft branches. There are more oil cells on new leaves compared to mature leaves. In Raman spectroscopy of mature leaf of oil cells, 1 675/726 cm-1(CC stretching/ring deformation) are a characteristic key band of terpinene-4-ol, 1 700/754 cm-1(CC stretching/ ring deformation) for γ-terpinene, 1 609 cm-1(CC stretching)for α- terpinene and 1 522/1 156/1 011 cm-1(CC stretching/C—C stretching/C—C in-plane rocking)for β-carotene. In Raman spectroscopy of new leaves oil cells, 745 cm-1 (ring deformation) is a characteristic key band of cis-sabinene hydrate, 1 609 cm-1 for α- terpinene and 1 522/1 160/1 008 cm-1 for β-carotene. The principal components are different in oil cells of new and mature leaves. It is the first report that there are cis-sabinene hydrate and β-carotene in oil cells of Melaleuca alternifolia. This method can be used for quality control and developmental research for Melaleuca alternifolia plant essential oil extraction.