To compare the chemical compositions between Dendrobium candidum (D. candidum) and Dendrobium nobile (D. nobile).Relative area and content of every chromatographic peak in the ammonic chloroform extracts of D. candidum were compared with those of D. nobile with high performance liquid chromatography-mass spectrometry.The relative area of alkaloids accounted for 2.34% and 41.87% in D. candidum and D. nobile, respectively. The relative area of 25 identical compositions took up 97.12% in the total area of D. candidum and 50.09% in that of D. nobile, and contents of 23 composition were higher in D. candidum than those in D. nobile.The quantity and contents of alkaloids are remarkably different between D. candidum and D. nobile. However, D. candidum has a higher quality than D. nobile in terms of the same chemical compositions.