Loneliness is a matter with which man has been faced all the time. In different fields such as Sufism, mysticism, psychology, philosophy and so on, a particular concept of the word is meant. Literature as the appearance arena of human thoughts and emotions has manifested these concepts and meanings in different ways. In the mystical Persian poetry, as the most prolific branch of Persian literature, loneliness has become mooted as a subject matter and a special attention has been paid towards the subject both in the classic and contemporary periods.In the persent paper, the authors examine the term of solitude in the mystical Persian poetry and conclude that its meaning in the classical Sufi poetry has been originated from early Islamic mysticism and is the same as literary meaning of the word.Of course there are some differences in the viewpoints of Sufi poets.Some of them like Sana yi emphasize more on the outward meaning of solitude but for some others like H a fedh the inward meaning of it is more important, while in the eye of Rumi both sides are of the same value.The concept of solitude in the classical branch of contemporary Sufi poetry which its rea l representative is Shahriar, follows the literary meaning of the term, while in the Sufi free poetry i.e. in the poetry of Sohr a b, it is under the influence of Buddhism and mostly used in the meaning of a spiritual silence necessary for contemplation and illumination.