An interpolation subset in the
boundary of a domain is a closed set in which every continuous (or smooth)
function can be extended as a holomorphic function inside the domain and
continuous (or smooth, respectively) up to the boundary. In this paper we
give some geometric description for submanifolds in the unitary group to
be interpolation sets for the domain obtained by taking polynomial hull of
the unitary group. In particular, we retrieved corresponding results on the
polydisc.