The phytochemical study of Piper pleiocarpum Chang ex Tseng led to the isolation of eighteen compounds (118), including ten lignanoids, galbelgin (1), (+) sesamin (2), denudatin A (3), hancinone (4), (7S,8S, 3'R)-Delta(8')-3,3',4-trimethoxy-3',6'-dihydro-6'-oxo-7.0.4',8.3'-lignan[(2S,3S,3aR)-2-(3,4-dimethoxyphenyl)-3,3a-dihydro-3a-methoxy-3-methyl-5-(2-propenyl)-6(2H))-benzofuranone] (5), (-)-(7R,8R)-machilin D (6), (1R,2R)-2-[2-methoxy-4-((E)-prop-1-enyl)phenoxy]-1-(3,4-dimethoxyphenyl)propyl acetate (7), piperbonin A (8), machilin D (9), 4-methoxymachilin D (10), one amide alkaloid, Delta(alpha,beta)-dihydropiperine (11), six polyoxygenated cyclohexenes, ent-curcuminol F (12), uvaribonol E (13), ellipeiopsol A (14), 1S,2R,3R,4S-1-ethoxy-2-[(benzoyloxy)methyl]cyclohex-5-ene-2,3,4-triol, 3-acetate (15), (+)-crotepoxide (16), (+)-senediol (17), and one benzoate derivative, 2-acetoxybenzyl benzoate (18). Their structures were established by spectroscopic data and by comparison with the literature. All the compounds were firstly isolated from P. pleiocarpum, while ten compounds 67, 910, 1215, 1718 were isolated from the genus Piper and the family Piperaceae for the first time. The chemotaxonomic significance of these compounds was also discussed. The isolation of compounds 67, 910 may be used as chemotaxonomic markers for the genus of Piper.