The electrical conduction mechanism for defect-perovskite LaTa₃O₉ was studied by D.C. polarization technique. The linear log (σ_dc) vs (time)^-1/2 relationship was observed, which means that diffusion process could be dominant for the electrical conduction. Total stored charges increased with increasing temperature depending on oxygen partial pressure (P_O2). Asymmetrical polarization measurements showed that the polarity of the electrode affected to the time dependence of σ_dc and leakage currents. The relationship between D.C. voltage and the leakage currents suggested that dominant electronic charges might change from electrons to holes with increasing temperature and P_O2.