To screen inhibitors on complement system from natural resources, micro-screening method was established by using hemolytic complement assay. Complement fixation reaction was carried out in the microplate system. For standard hemolysis (50% hemolysis) of the classical pathway (CP), hemolysin and complement serum were diluted to 1/75∼1/100 and 1/80∼1/120, respectively, when sheep erythrocytes were 5.0×10^8 cells/㎖. In case of the alternative pathway (AP), complement serum was diluted to 1/5 and EGTA and Mg^(2+) were added 4 mM, 4∼8 mM, respectively, when rabbit erythrocytes were 4.0×10^8 cells/㎖. Dimethyl sulfoxide was used for the assay of non-aquous soluble compounds or extracts and its final concentration was not more than 1%. Three phenylpropanoids showed anticomplementary activities in proportion to the concentration for both pathways and rosmarinic acid exihibited the highest inhibitory activities: 5.4±3.6%(0.063 mM)∼95.8±0.2%(0.5 mM) and 35.1±0.9%(0.063 mM)∼95.6±1.1%(1 mM) on the CP and the AP, respectively.