We have performed a comprehensive study of electrical properties at high temperatures of single-phase BiFeO3 nanoparticles. Our results revealed a strong dependence of electrical resistivity behavior and activation energy on thermal cycle due to adsorption/desorption of water molecules. Ionic conductivity due to oxygen vacancies as well as H+ ions should dominate the electronic current after the initial heating and cooling cycle explaining the change in the charge transport properties due to thermal, temperature, and atmosphere history. Electronic structure simulations indicated that the characteristics of the conductivity in the original sample is consistent with band-to-band transitions, expected in a material rich in oxygen.