A bicrystalline titanium dioxide nanofiber with enhanced photocatalytic activity was synthesized from potassium titanate K2Ti 2O5 via ion exchange and calcination. The nanofiber has a core-shell crystalline structure with a thin TiO2(B) phase sheathing the anatase core, as characterized by X-ray diffraction, Raman spectroscopy, and high-resolution transmission microscopy (HRTEM). From HRTEM and local electron diffraction patterns, the two crystalline phases form a coherent interface with the 0.34-nm spacing between the (102) planes of TiO2(B) matching that between the anatase (101) lattice planes. The core-shell anatase/TiO 2(B) nanofiber shows enhanced photocatalytic activity in iodine oxidation reaction with a 20-50% increase in extent of reaction compared to either single-crystal anatase or single-crystal TiO2(B) nanofibers. Anatase and TiO2(B) have the same band gap value of 3.2 eV, while theoretical calculations show the conduction band (CB) and valence band (VB) energies in anatase are both lower than the corresponding CB and VB energies in TiO2(B). The enhanced photocatalytic property may be due to enhanced and concerted charge mobility toward or away from the anatase/TiO2(B) interface. The special structure-property relationship can provide a new strategy to design and fabricate efficient photocatalytic and photovoltaic materials.