Abstract: AimTo analyze and compare the compositions in essential oils from branches and leaves of Rhododendron simsii Planch. and Rhododendron naamkwanense Merr. MethodsEssential oils were extracted by water distillation according to Chinese Pharmacopoeia and analyzed by capillary gas chromatography-mass spectrometry as well as chemometrics resolution method and authentic compounds. The relative contents of each component in the essential oils were obtained by normalization of peak areas. ResultsA total of 124 components were identified, of which 48 compounds were existed in both of the samples. Ninety four compounds accounted for 84.47% of the essential oil from Rhododendron simsii Planch. and seventy eight components accounted for 90.25% of the total essential oil from Rhododendron naamkwanense Merr. were identified. 72.76% and 88.07% of the components in Rhododendron simsii Planch and Rhododendron naamkwanense Merr., respectively, included oxygen element. They are mainly terpenol, acids and esters. 1-octen-3-ol (4.00%, 7.90%), 1,6-octadien-3-ol, 3,7-dimethyl- (12.60%, 3.48%), 9,12,15-octadecatrienoic acid,［Z,Z,Z］- (1.15%, 45.34%), phytol (15.21%, 8.56%), p-menth-1-en-8-ol (2.15%, 3.29%), and 9,12,15-octadecatrienoic acid, ethyl ester,［Z,Z,Z］- (9.16%, 8.01%) were their common main compounds, which accounted for 44.27% and 76.58% of the total amount of the two essential oil samples, respectively. In addition, n-hexadecanoic acid (7.73%), 9,12-octadecadienoic acid (1.85%) and tetracosanoic acid, methyl ester (1.38%) were also the main compounds in essential oil from Rhododendron simsii Planch. Conclusion Much higher reliability and accuracy were obtained with the help of chemometrics resolution method and authentic n-alkane standard solutions than those of using GC-MS alone.