Target mass effects in QCD Bjorken sum rule

We investigate the target mass effects in QCD Bjorken sum rule. The magnitude of the target mass correction is estimated in a variety of methods employing positivity bound as well as the experimental data for the asymmetry parameters. It turns out that the target mass correction is sizable at low Q2 of the order of a few GeV2, where the QCD correction is significant. We show that there exists uncertainty due to target mass effects in determining the QCD effective coupling constant αs(Q2) from the Bjorken sum rule.