Temperature and oxygen partial pressure, P(O-2), dependence of oxygen nonstoichiometry of LaNi0.6Fe0.4O3 - delta, which is a new candidate cathode material for solid oxide fuel cells, has been determined by the equilibrium thermogravimetry. The P(O-2) and temperature dependence of the electrical conductivity of LaNi0.6Fe0.4O3 - delta has also been measured. It has been clarified that the oxygen content, 3 - delta of LaNi0.6Fe0.4O3 - delta a at temperatures between 300 degrees C and 700 degrees C under 10(-4) bar <= P(O-2) <= 1 bar is around 2.90, which can be explained by Ni and Fe valence of +2 and +4, respectively. Temperature and P(O-2) dependence of the oxygen nonstoichiometry and the electrical conductivity is small for LaNi0.6Fe0.4O3 (- delta), which can be ascribed to small variation of the average valence of B-site ion by temperature and P(O-2) due to occurrence of charge compensation between Ni ion and Fe ion. The easy occurrence of the charge compensation corresponds to hopping conduction with small, temperature and P(O-2) independent activation energy. By combination of oxygen nonstoichiometry and electrical conductivity, it has been clarified that LaNi0.6Fe0.4O3 (- delta) a is p-type conductor with mobility of 0.257 cm(2) V-1 s(-1), which is independent on temperature and P(O-2). Hole concentration at temperatures between 300 degrees C and 800 degrees C under -4 <= log(P(O-2)/bar) <= 0 is 3-4 x 10(21) cm(-2). (C) 2015 Elsevier B.V. All rights reserved.