An air filter for an internal combustion engine having a rigid type ceramic filter element made by foaming oxygen-rich ceramic powder for creating a plurality of pass-through holes. In this way, the incoming air obtains a thorough contact with the oxygen-rich powder. Meanwhile, the material of the oxygen-rich ceramic releases negative ions to activate the air entering into the internal combustion engine. Moreover, nano-sized platinum black is coated to the surface of the pass-through holes of the ceramic filter element. So, the incoming air passing through the pass-through holes of the ceramic filter element is catalyzed in chemical reactions to divide the water molecule cluster into smaller particles. Meanwhile, the freedom of water molecule is increased to permit an instant decomposition of oxygen and nitrogen molecules, a complete combination with the fuel injected into the internal combustion engine, and a thorough mixing and a better combustion efficiency.