Change in the lattice parameters of La0.6Sr0.4Co1-yFeyO3-delta (y=0.2, 0.4, 0.6 and 0.8) was observed by in-situ XRD under the various temperature and oxygen partial pressure conditions for thermo-chemical expansivity study. By combination of the lattice parameters and oxygen non-stoichiometry, the linear thermal expansion rates were formulated in each compound. The obtained formulas are expressed as a linear function of temperature and oxygen deficiency with the standard deviations from measured data less than 1.2%. Based on the formulas, apparent thermal expansions were separated into thermally induced part and chemically induced part. Thermal expansion coefficient alpha(th), which is proportional constant for temperature, is increased with increasing Co content in La0.6Sr0.4Co1-yFeyO3-delta while chemical expansion coefficient alpha(chem), which is proportional constant for oxygen deficiency, shows very small dependence on the composition. Increase in apparent thermal expansion with increasing Co content in La0.6Sr0.4Co1-yFeyO3-delta was caused by the combination of alpha(th) and alpha(chem). (C) 2011 Elsevier B.V. All rights reserved.