In a recent work Grimaud et al. [J. Electrochem. Soc., 159, B683 (2012)] have shown that it is possible to insert water in fast oxygen ion conducting oxide with high oxygen non-stoichiometry, such as Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF5582) and create the possibility of proton conductivity in them. Here we study the hydration/dehydration kinetics of BSCF5582 by electrical conductivity relaxation technique in 500-900 degrees C range. The values of proton diffusivity ((D) over tilde (iH)) and oxygen diffusivity ((D) over tilde (vH)) were extracted by applying the concept of decoupled diffusion of H and O species upon hydration/dehydration, and (D) over tilde (iH) and (D) over tilde (vH) were obtained from the non-linear least square (NLS) fitting of conductivity relaxation data. The decoupled diffusion in BSCF5582 was verified by comparing its conductivity relaxation profile with the simulated conductivity relaxation profiles for proton conducting oxides with different (D) over tilde (vH)/(D) over tilde (iH) ratios. (D) over tilde (iH) of BSCF5582 were comparable with other proton conducting perovskite-type oxides. Similarly, (D) over tilde (vH) values obtained in this work in humid air atmosphere [-2.9 <= log(pH(2)O/atm)<=-2.29] were similar to 10(-4) cm(2)s(-1) and they were comparable to the (D) over tilde (chem) values obtained in dry air [-0.96 <= log(pO(2)/atm)<=-0.64] in previous report. (C) 2013 The Electrochemical Society. All rights reserved.