Abstract: The chemical constituents and antitumor activity of Rhododendron decorum were studied. Twenty compounds were isolated from the EtOAc extract of this plant by silica gel, sephadex LH-20 and RP-18 column chromatography, and CCK-8 method were used to test the antitumor activity in vitro. They were identified as decorumtone (1), confluentin (2), o-methy-llasiodiplodin (3), daurichromenes A (4), arthproliferin B (5), grayanotoxin-Ⅰ (6), grayanotoxin Ⅳ (7), (Z)-9,10-dihydroxy-6,10-dimethyl-5-undecen-2-one (8), 8-hydroxy-6,7-dihydrolinalool (9), (E)-2,6-dimethyl-2,7-octadiene-1,6-diol (10), 9-hydroxy-4,7-megastigmadien-3-one (11), vomifoliol (12), dehydrovomifoliol (13), euscaphic acid (14), kaempferol (15), afzelin (16), avicularin (17), aromadedrin-3-O-α-L-arabinopyranoside (18), noreugenin (19), scopoletin (20) on the basis of physicochemical properties and spectral data. Those compounds have no significant activity against to the cell lines A-549, HepG2, Hela-60, MDA-MB-68. Compound 1 was a new natural product, Compounds 1−5, 7−20 were isolated from Rhododendron decorum. for the first time.