The paper presents the method of investigation into the level of air pollution caused by heavy metals in some industrial areas and traffic sites in Northern Vietnam towns by magnetism-based observation. There is a large content of magnetic material in air dust. According to this method, the magnetic property and the heavy-metal concentration are studied by Vibrating Sample' Magnetometer (VSM) and Atomic Absorption Spectroscopy (AAS), respectively. Through the magnetic property, the air pollution level of heavy metals in investigated areas is enabled for assessment. The results are obtained in Hanoi, Hai Phong, Bac Ninh and Hung Yen.