  In this paper we discuss the solvability of Langevin equations with two
Hadamard fractional derivatives. The method of this discussion is to study the
solutions of the equivalent Volterra integral equation in terms of Mittag-
Leffler functions. The existence and uniqueness results are established by
using Schauder fixed point theorem and Banach fixed point theorem respectively.
An example is given to illustrate the main results.
