A slide assembly includes a first slide member having a guiding base and a lock portion, a second slide member having a first slide segment and a second slide segment, a third slide member movably mounted on the second slide segment, an aid-sliding member slidably connected between the first slide member and the first slide segment, and a positioning device connected to the second slide member. The positioning device includes an elastic member and a positioning member which is movable by a force of the elastic member, so that two ends of the positioning member are respectively located corresponding to the guiding base and the third slide member. The positioning member is engaged with the lock portion when the second slide member is moved relative to the first slide member, and is disengaged from the lock portion when the third slide member is retracted relative to the second slide member.