We study the impact of third-order QCD corrections for several kinematic moments of the inclusive semileptonic B decays, to first order in the 1/mb expansion. We consider the first four moments of the charged-lepton energy ER spectrum, the total leptonic invariant mass q2 and the hadronic invariant mass {M}_X^2 . No experimental cuts are applied. Our analytic results are obtained via an asymptotic expansion around the limit mb ~ mc. After converting the scheme for the bottom mass to the kinetic scheme we compare the size of higher QCD corrections to the contributions from 1/ {m}_b^2 and 1/ {m}_b^3 power corrections and to the relative uncertainties.