Given a set P of n points in the plane, the unit-disk graph G r (P ) with respect to a parameter r is an undirected graph whose vertex set is P such that an edge connects two points p, q ∈ P if the Euclidean distance between p and q is at most r (the weight of the edge is 1 in the unweighted case and is the distance between p and q in the weighted case). Given a value λ > 0 and two points s and t of P , we consider the following reverse shortest path problem: computing the smallest r such that the shortest path length between s and t in G r (P ) is at most λ. In this paper, we present an algorithm of O( λ • n log n) time and another algorithm of O(n 5/4 log 7/4 n) time for the unweighted case, as well as an O(n 5/4 log 5/2 n) time algorithm for the weighted case.