  We discuss the gauge invariance of quark-quark potential in QCD in the
perturbative treatment, and show that the gauge dependence of the quark-gluon
interaction cannot be eliminated. Therefore, the quark-quark potential cannot
properly be written in terms of physical variables in the perturbation theory.
This is in contrast to the QED case in which the gauge invariance of the
electron-photon interaction is guaranteed by the current conservation. As an
example, we show that the different choices of the gauge fixing give different
Coulomb interactions when the fermion current is not conserved. Also, we
examine a possible existence of $QG-$state (one quark$-$one gluon)
corresponding to the conserved color current, which should have a fractional
electric charge.
