Abstract: Eight plant species were picked randomly and their aqueous extracts have been screened to know their effects on the phagocytic capability and intracellular killing of E. coli bacteria by rat peritoneal macrophages. Macrophage cultures were incubated with different concentration of each plant extract for 1 hour. Among these aqueoud extracts, Ageratum conyzoides and Malastoma melabathricum inhibited the phagocytic capability and intracellular killing of E. coli compared with controls. Elicited (activated) cells have more phagocytic capability and intracellular killing than the resident (normal) macrophages. There were no differences in the viability of cells between treated cells with extract and controls.