The present invention relates to a sliding device (100) for a vehicle seat, comprising a pair sliding tracks (10), each including a lower rail (20) and an upper rail (30), which allow to obtain an improved stability and to reduce the sliding efforts when the upper rails slide relative to the lower rails. Each upper rail is constrained to a respective lower rail and is free to slide relative thereto, balls (70) are arranged between said upper rail and said lower rail, and said upper and lower rails are shaped so as to define a lower and an upper ball guides (72, 74) on each side thereof. The design of said upper and lower rails at said lower and upper ball guides (72, 74) is such that efforts during relative sliding movements of the rails are reduced, while enhancing stability of the rails and preventing deformations thereof.