This research is concerned with the issue of Viola's – the heroine - disguise in Twelfth Night. This young woman, who has closed the sad chapters of her life, decides to begin a new life, as if she had not known desperation by disguising as a young man named ''Cesario''. In this play, we notice that disguise turns from a simple device to a complicated one. At the beginning, Viola's aim is to protect herself in a country where she knows no one. But later, disguise comes to mean more than this. Cesario begins to dominate Viola, the characters and the play. He teaches everyone lessons in life about true love, faithfulness, sacrifice for the happiness of the others, and selflessness. Also, he removes the false masks of the others. Sebastian's appearance gives Viola the strength to admit, before all people, her real identity. This is what helps to solve a lot of ambiguity and questions for us and the characters. Viola's strength does not lie in her disguise as a man but in the way that she uses disguise and directs it.