Children's mental representations about physical concepts and phenomena play a vital role in the learning process. This is confirmed by the data derived from relevant researches which demonstrate that the students formulate incompatible ideas compared with the scientific ones. In this research we investigate the representations of 14-15 years old students about the magnetic field. One hundred and sixteen students participated in the research and the directive individual interview was the technique that we used to collect the empirical data. The results indicate that the children face difficulties in the comprehension of the nature as of the properties of the magnetic field.