Abstract: Dendrobium crepidatum Lindl.ex Paxt.was a perennial epiphytic herb with high health and medicinal value in Dendrobium SW,Orchidaceae.The components and contents of alkaloids were studied by UPLC-Q-TOF-MS from the stems of D. crepidatum.Fifteen alkaloids and bibenzyls components were identified from the stems,in which twelve components were alkaloids and three components were bibenzyls.There were two components with contents more than 50 μg/g,crepidine174.844 μg/g and crepidamine 92.862 μg/g respectively;5-50 μg/g of 15 components:dendrocrepidine B,dendrocrepidine D,dendrocrepine, dendrocrepidine C, and homocrepidine B;crepidatin,N-isopentenyl-dendrobinium,dendrobine,N-isopentenyl-dendroxinium,moscatilin,dendrocrepidine E,crepidatuol A,and nobilonine were found in 15 components less than 5 μg/g.Four sesqueterpenoid alkaloids were firstly discovered from D. crepidatum.Alkaloids were mainly composed of octahydroindolizine alkaloids.

Key words: Orchidaceae, Dendrobium, alkaloids, sesquiterpenoid, octahydroindolizine, UPLC-MS