  We study the following class of nonlinear Choquard equation, $$ -\Delta u
+V(x)u =\Big( \frac{1}{|x|^\mu}\ast F(u)\Big)f(u) \quad \mbox{in} \quad \R^N,
$$ where $0<\mu<N$, $N \geq 3$, $V$ is a continuous real function and $F$ is
the primitive function of $f$. Under some suitable assumptions on the potential
$V$, which include the case $V(\infty)=0$, that is, $V(x)\to 0$ as $|x|\to
+\infty$, we prove existence of a nontrivial solution for the above equation by
penalization method.
