  A magnetic order in orthorhombic GdCu$_2$ was investigated via a single
crystal neutron diffraction with thermal neutron. Magnetic peaks were observed
at incommensurate positions described by the ordering vector
$q$=(${\delta}$,~1,~0) with ${\delta}$=0.678 at 4.6~K. This ordering vector is
close to the commensurate one with $q_{\rm c}$=(2/3,~1,~0) reported earlier,
but clearly deviates. The incommensurate nature of the magnetic order in
GdCu$_2$ is further corroborated by the peak shift with temperature below
$T_{\rm N}$.
