Atomistic and electronic structures of PbTiO3 nanowires with atomically sharp edges consisting of (100)/(010) surfaces using first-principles calculations. Ferroelectricity is enhanced at the PbO-terminated edge in the nanowire because the Pb-O covalent bond that predominates the ferroelectric distortions is partially strengthened. On the other hand, a significant suppression is observed in the TiO2-terminated nanowire. Surprisingly, the smallest (one-unit-cell cross- section) PbO-terminated nanowire can keep ferroelectricity, while ferroelectricity disappears in the TiO2-terminated nanowires with a diameter of smaller than 17 Å. The ferroelectricity is recovered by axial tension, where the thinner nanowire requires the higher critical strain.