Hemical variability of essential oils in Chenpi or called Pericarpium Citri Reticulatae(PCR)and Qingpi or called Pericarpium Citri Reticulatae Viride(PCRV)from the same source was investigated by gas chromatography-mass spectrometry(GC-MS)compiled with Automated Mass Spectral Deconvolution & Identification System(AMDIS).PCRV and PCR were collected once a month during July-December in 2011 from the identical area and the cultivar as Citrus Reticulata Dahongpao ofC.reticulata Blanco.The oil components were identified by their purified mass spectra and Kováts retention indices(RIs).A total of 67,77,66,51,46,and 59 compounds representing 89.856%,92.151%,97.881%,97.738%,97.229%,and 97.897% of their total relative contents,respectively in the oils of PCRV and PCR were discerned.The oils from PCRV and PCR varied considerably both qualitatively and quantitatively.Chemical changeability of six samples differed with each other,to a degree.The chemotype as D-limonene/γ-Terpinene/Linalool(55.111-77.659%/6.579-7.841%/1.197-7.773%)was differentiated for essential oils of PCRV and PCR from C Reticulata Dahongpao.The study manifests AMDIS can efficiently enhance the accuracy of quantitative and qualitative analyses by extracting information from chromatograms and mass spectra.The results have some meanings to clarify the similarities and differences in bioactive compounds as volatile oils of PCRVand PCR,and to expound the scientific essence of"One material used as two kinds of Chinese materia medica(CMM)" such as PCRV and PCR in the end.