Parametric line profile analysis has been used to separate size and strain contributions to the peak broadening of in situ X-ray diffractograms recorded during isothermal annealing of nanocrystalline SnO 2 materials. Of five kinetic models for isothermal crystallite growth, the simplified generalised parabolic model was found to be the closest to transmission electron microscopy (TEM) crystallite sizes resulting in expected (exponential) relaxation of strain. Crystallite growth and strain evolution of pure and Pd-doped SnO 2 has been compared and discussed regarding possible growth mechanisms. It was shown that lattice strain, despite being very low, leads to overestimation of the activation energy for crystallite growth, if not considered in integral breadth analysis. • parametric line profile analysis applied to calculate size and microstrain. • kinetics of crystallite growth and microstrain evolution upon isothermal annealing. • effect of Pd doping on crystallite growth and microstrain relaxation in SnO 2 . • crystallization of amorphous phase under isothermal annealing.