[ $Ti_{1-x}W_xO_{2-y}$ ]solid solutions with compositions of x = 0.01(TW-1), x = 0.02(TW-2), x = 0.03(TW-3) and x = 0.04(TW-4) were prepared at 1,073 K in air under atmospheric pressure. All the solutions exhibited tetragonal symmetries. Nonstoichiometric chemical formulas have been obtained from oxidation-reduction titration and the partial substitution of $W^{6+}$ ions mainly caused the formation of $Ti^{3+}$ ion, rather than oxygen excess. Resistivities of the samples were highly dependent on humidity. The increase of the W amount resulted in an increase of $Ti^{3+}$ content, decrease of resistivity values and finally degradation of photocatalytic activities.