An environment-conservative fuel economizer includes a hollow tubular member and at least one ring member. The tubular member has an internal surface forming a reduced neck section. The ring member is mounted to an end of the tubular member. The ring member forms a plurality of cut-off slits, which defines a plurality of deformable leaves. The neck section of the tubular member forms a flow-accelerating passage, which increases speed of air flow passing therethrough to induce secondary combustion. The leaves are allowed to selectively expand/contract to effect complete combustion and reduce pollution. The fuel economizer is installed between an automobile air filter and engine air-intake tube to use the suction force induce by air intake of cylinder to draw in air so that the mixture density of air and atomized fuel is intensified to effect complete combustion of fuel and enhance instantaneously engine torque and reduce fuel consumption.