An analytic series solution is developed in this paper for the electromagnetic field scattered by a confocal semielliptic cylinder consisting of dielectric and conductor for a transverse magnetic polarized line source illumination. The scattered field is represented in terms of Mathieu functions with unknown coefficients. By applying appropriate boundary conditions the unknown coefficients are obtained. Some numerical results are shown for mutual interactions between dielectric and conductor with the different eccentricities and permittivities. ¿ 2000 American Geophysical Union