  In this paper, we study the 't Hooft type instantons in eight dimensions,
which satisfy the (anti)self-dual equations $F\wedge F=\pm\ast_8F\wedge F$.
Using various designs of such instantons, we find new soliton solutions to the
low-energy effective theory of the heterotic fivebrane. We investigate
conditions under which these instanton configurations can be identified with
the $D$-instantons embedded in the $D7$-brane world volume. Finally, we discuss
the relationship between eight-dimensional periodic instantons and monopoles.
