In this paper, we investigate compact Legendrian submanifolds L in Sasakian manifolds M, which have extremal volume under Legendrian deformations. We call such a submanifold L-minimal Legendrian submanifold. We derive the second variational formula for the volume of L under Legendrian deformations in M. Applying this formula, we investigate the stability of L-minimal Legendrian curves in Sasakian space forms, and show the L-instability of L-minimal Legendrian submanifolds in S 2n+1 (1). Moreover, we give a construction of L-minimal Legendrian submanifolds in R 2n+1 (−3). 1. Introduction. In [10], [11], Y. G. Oh introduced the notion of Hamiltonianminimal (H-minimal) Lagrangian submanifolds in Kähler manifolds. Such a submanifold is a critical point of the volume functional under the Hamiltonian deformation. This is an extension of the notion of minimal submanifold, and has been studied by many authors (for example, [7], [8], [11], [14] and see references therein). An H-minimal Lagrangian submanifold is called Hamiltonian-stable (H-stable) if the second variation is non-negative for any Hamiltonian deformation. Oh studied H-stablity of some examples of H-minimal Lagrangian submanifold in a specific Kähler manifold ([10], [11]). For example, the real projective space RP n and the Clifford torus in CP n , and the standard tori in C n are H-stable. Besides these examples, Schoen and Wolfson studied the H-stablity of two-dimensional H-minimal Lagrangian cones ([14]), and Iriyeh studied the three-dimensional case ([8]). Furthermore, in [1], Amarzaya and Ohnita proved that all compact Lagrangian submanifolds with parallel second fundamental form in C n and CP n are H-stable.On the other hand, there is a notion of Sasakian manifolds, which is an odd-dimensional counterpart to Kähler manifolds. In Sasakian manifolds, we consider Legendrian-minimal (Lminimal) Legendrian submanifolds which correspond to H-minimal Lagrangian manifolds in Kähler manifolds. An L-minimal Legendrian submanifold is a critical point of the volume function under the Legendrian deformation (for more details, see Section 3). In [7], [8], the authors constructed examples of L-minimal Legendrian submanifolds in odd-dimensional unit spheres (in [7], such submanifolds are called C-minimal). Moreover, they show that a certain L-minimal Legendrian submanifold in a Sasakian manifold is related to an H-minimal Lagrangian submanifold in a Kähler manifold. For example, the cone over a Legendrian