Guided by anti-complementary activity, silica gel, Sephadex LH-20 and reversed-phase column chromatographies were used for fractionation and isolation of the ethyl acetate and n-butanol soluble fractions of Pogostemon cablin. Eighteen compounds were obtained, including 15 flavonoids: 5-hydroxy-3,7,3',4'-tetramethoxyflavone (1), 5-hydroxy-7,3',4'-trimethoxyflavanone (2), 5,4'-dihydroxy-3,7,3'-trimethoxyflavone (3), 5-hydroxy-3,7,4'-trimethoxyflavone (4), 5,4'-dihydroxy-7,3'-dimethoxyflavone (5), luteolin (6), quercetin-7,3', 4'-trimethyl ether (7), ermanine (8), 3,5,7- trihydroxy-3', 4'-dimethoxyflavone (9), quercetin (10), apigenin (11), kaempferol (12), 5-hydroxy-7,3',4'-trimethoxyflavone (13), kaempferol-7-O-beta-D-glucopyranoside (14) and kaempferol-3-O-beta-D-glucopyranoside-7-O-alpha-L-rhamnoside (15); one triterpenoid: oleanic acid (16); and 2 phenolic acids: vanillic acid (17) and benzylalcohol (18). The isolation of 5, 7, 8, 12-15 and 18 from the Pogostemon genus is reported for the first time. All isolates were evaluated for their in vitro anti-complementary activities on the classical pathway and alternative pathway. And the targets of the most potent constituent in complement activation cascade were identified using complement-depleted sera. Compounds 3, 7, 10, 12 and 16 exhibited anti-complementary activities toward the classical pathway and alternative pathway (CH50 0.072-1.08 g x L(-1), AP50 0.39-0.49 g x L(-1)), while 5 and 6 showed inhibitory effect on the classical pathway only. Mechanism study indicated that 7 interacted with C1q, C2, C5 and C9 components.