In this article, we consider a closed rank one Riemannian manifold M without focal points. Let P (t) be the set of free-homotopy classes containing a closed geodesic on M with length at most t, and #P (t) its cardinality. We obtain the following Margulis-type asymptotic estimates:where h is the topological entropy of the geodesic flow. In the appendix, we also show that the unique measure of maximal entropy of the geodesic flow has the Bernoulli property.