Abstract: In this talk we study the pions dispersion relations in the presence of external magnetic fields and at finite quark chemical potential and temperature. Here we find the effective action of a two-flavor NJL model with four Fermi interaction and then using the derivative expansion of this action derive the form factors in the kinetic terms of the meson action. With this method we can find the refraction index and the masses of the neutral pions as well as the pion decay constants in terms of temperature, chemical potential and external magnetic fields.