The interaction potential of a two-dimensional system of excitons with spatially separated electron-hole layers is considered in the strong magnetic field limit. The excitons are assumed to have free dynamics in the x-y plane, while being constrained or 'polarized' in the z direction. The model simulates semiconductor double layer systems under strong magnetic field normal to the layers. The residual interaction between excitons exhibits interesting features, arising from the coupling of the

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... ter-of-mass and internal degrees of freedom of the exciton in the magnetic field. This coupling induces a dynamical dipole moment proportional to the center-of-mass magnetic moment of the exciton. We show the explicit dependence of the inter-exciton potential matrix elements, and discuss the underlying physics. The unusual features of the interaction potential would be reflected in the collective response and non-equilibrium properties of such system.