The main purpose of this paper is to construct the THEME system of Myanmar following the system network for Theme in English proposed by Halliday (1985, 1994; Halliday and Matthiessen 2004, 2014) within the framework of Systemic Functional Linguistics. It is found that the THEME system of Myanmar consists of two sub-systems: Theme status and Theme composition. For the former, there are two major types: unmarked and enhanced Themes, while for the latter, Theme can be presented in two ways: simple and multiple Themes. Unmarked Themes in Myanmar clauses are Subject, Complement, Adjunct, hypotactic clause, Predicator (only in imperative), and Ba-element (only in interrogative). The enhanced Theme in Myanmar contains two major types: equative or preposed attribute. Multiple Theme includes textual, interpersonal and topical Themes which can be chosen as a point of departure of the clause. The findings may shed light on the realization of the textual metafunction of Myanmar language.