A vehicle seat sliding device includes a lower rail adapted to be fixed to the floor of the vehicle, an upper rail adapted to be fixed to the vehicle seat and mounted on the lower rail for forward and rearward movement, and a releasable lock mechanism disposed between the lower rail and the upper rail for locking the upper rail. The lock mechanism has a lock lever disposed within sections of the upper and lower rails and extending forward and rearward, with the lock lever being movably mounted on the upper rail. A nail portion is formed on the lock lever and is adapted to be selectively fitted into engaging holes formed on the upper and lower rails from inside the upper and lower rails toward outside. An urging mechanism is positioned within the sections of the lower and upper rails for urging the lock lever toward its locking condition, and an operating mechanism operates the lock lever.