The mystical language of Mulānā Jalāl-al Din Rumī is distinct and special. He utilizes linguistic signs, significants, significances and signifieds for expressing his mystical ideas. One of the most applied signs, in his poems, is sun. He relates it, as a significant, to different signifieds or different features of a signified. In mystical texts, sun is one of common linguistic signs, but Rumī uses it according his own mystical experiences and doesn't imitate his predecessors. So, sun, as a linguistic sign, includes a widespread field of significance and suggests different ideas to readers in different poems. The present article tries to show applications of the term of sun, its meaning and its various significances in the works of Mulānā Jalāl-al Din Rumī, in this way it is possible to have a better interpret of some of his poems.