The unit graph of a ring
with nonzero identity is the graph in which the vertex set is
, and two distinct
vertices
and
are adjacent
if and only if
is a unit in
.
In this paper, we derive several necessary conditions for the nonplanarity of the unit
graphs of finite commutative rings with nonzero identity, and determine, up to
isomorphism, all finite commutative rings with nonzero identity whose unit graphs
are toroidal.