We investigate whether the discrete energy levels and the high peak absorption in quantum dots (QDs) provide an opportunity for increasing the electro-optic and nonlinear optical properties. For this purpose we calculate the electrorefraction spectra of QDs starting from the Luttinger-Kohn Hamiltonian and using a plane-wave expansion for solving the eigenstates of the QD. For a pyramidal InAs/GaAs quantum dot, we find a high peak electrorefraction of 0.35 for TE-polarization, which is 35x larger than in a quantum well. In the tail of the quantum dot absorption spectrum, we find an electrorefraction of 1.3.10-2 at an absorption loss of 0.15 dB/cm. Finally we investigate the refractive index variation due to state filling in InAs/InP cylindrical quantum dots.