  An exact solution of the low-energy string theory representing static,
spherical symmetric dyonic black hole is found. The solution is labeled by
their mass, electric charge, magnetic charge and asymptotic value of the scalar
dilaton. Some interesting properties of the dyonic black holes are studied. In
particular, the Hawking temperature of dyonic black holes depends on both the
electric and magnetic charges, and the extremal ones, which have nonzero
electric and magnetic charges, have zero temperature but nonzero entropy. These
properties are quite different from those of electrically (or magnetically)
charged dilaton black holes found by Gibbons {\it et al.} and Garfinkle {\it et
al.}, but are the same as those of the dyonic black holes found by Gibbons and
Maeda. After this paper was submitted for publication, D. Wiltshire told us
that solutions, eqs.(22)-(28), are related to Gibbons-Maeda dyonic black hole
solutions by a coordinate transformation and some parameters reparametization
\cite{26}. And, we were also informed that many of our results were previously
obtained by Kallosh {\it et al.} \cite{27}. The dyonic black hole solutions,
eqs.(22)-(28), are also related to those of reference \cite{27} by another
coordinate
