We have analysed high dispersion spectra of the supergiant γ Cyg (F8 Ib). On the basis of the curve of growth method it has been shown that there is no dependence of microturbulent velocity ξt on excitation potentials of spectral lines. Using model atmospheres we considered about 100 Fe I lines and found that no constant value ξt makes possible to remove the systematic discrepancy in iron abundance between groups of lines with different equivalent widths. The depth dependence of microturbulence in the atmosphere is investigated. It is shown that parameter ξt increases outwards from about 0-1 km/s at the optical depth τ5000 = 0.2 to 10 km/s at the depth τ5000 = 10-3. Deducted function ξt (τ5000) gives the same iron abundance log ε(Fe) = T = 7.45 ± 0.05 for all groups of Fe I lines. The detailed analysis will be published in Izv. Crimean Astrophys. Obs.