Changes in network structures of ${alpha}-Nb_2O_5$ in the X MgO+(1-X) ${alpha}-Nb_2O_5$ solid solutions occurring as the MgO doping level (X) was varied were investigated by means of infrared spectroscopy and X-ray analysis. X-ray diffraction revealed that all the synthesized specimens have the monoclinic structure. The FT-IR spectroscopy showed that the system investigated forms the solid solutions in which $Mg^{2+}$ ions occupy the octahedral sites in parent crystal lattice. Electrical conductivities were measured as a function of temperature from 600 to $1050{circ}$ and $P_{O2}$ form $1{ imes}10^{-5}$ to $2{ imes}10^{-1}$ atm. The defect structure and conduction mechanism were deduced from the results. The $1}n$ value in ${alpha}{propto}{P_{O2}^{1}n}}$ is found to be -1/4 with single possible defect model. From the activation energy ($E{alpha}$ = 1.67-1.73 eV) and the1/n value, electronic conduction mechanism is suggested with a doubly charged oxygen vacancy.