We have performed first-principles calculations to study the structural and polarization properties of short-period SrZrO3/SrTiO3 (SZO/STO) superlattices. The in-plane lattice constant of the superlattice expands as the SZO ratio increases. The SZO/STO superlattices are found to exhibit typical ferroelectricity in spite of the paraelectric nature of SZO and STO, and the magnitude of polarization depends on the c/a ratio of the superlattice, in agreement with the experiment. Both SZO and STO layers in the superlattices are strongly polarized, and the polarization contribution from SZO layers exceeds that from STO layers.