  We discuss the possible target mass corrections in the QCD analysis of
nucleon's spin-dependent structure functions measured in the polarized
deep-inelastic leptoproduction. The target mass correction for the QCD Bjorken
sum rule is obtained from the Nachtmann moment and its magnitude is estimated
employing positivity bound as well as the experimental data for the asymmetry
parameters. We also study the uncertainty due to target mass effects in
determining the QCD effective coupling constant $\alpha_s(Q^2)$ from the
Bjorken sum rule. The target mass effect for the Ellis-Jaffe sum rule is also
briefly discussed.
