Activity-guided fractionation for complement inhibitors led to the isolation of 24 known compounds from Anchusa italica. Chemical types include eight megastigmane compounds, five triterpenoid compounds, five lignan compounds, three flavonoid compounds, two alkaloid compounds and one phenthyl alcohol compound. Among which, a lignan (medioresinol), an alkaloid (5-hydroxypyrrolidin-2-one) and a flavonoid (5-hydroxyl-3', 4', 6, 7-tetramethoxy flavone) exhibited better anticomplementary effects with CH50 values ranging from 0.07 to 0.82 mM, which are plausible candidates for developing potent anticomplementary agents.