The `Alejandro` singer took action against Russian Anastasia Obukhova, 26, who had threatened to shoot her in the head.
In a letter obtained by the star`s management, the New York-based student wrote: "You come to my dreams. I want to die and I want to die together with you."
The letter continues with Obukhova referencing Mark Chapman, who murdered Beatles legend John Lennon in 1980 by shooting him four times outside his New York apartment.
She wrote: "I am not Mark Chapman. It is not only you who will die. I will shoot a bullet through my head too."
Under the terms of the restrainingorder, Obukhova is banned from going within 500 metres of LadyGaga but the eccentric singer - real name Stefani Germanotta - has stepped up her security in the wake of the alleged death threat.
A source told The Sun newspaper: "Security is always tight around her but even more so now she`s on tour. Her team won`t take any chances."