Scriabin`s output is often split into three periods.: Op. 1-29 (1886-1901), Op. 30-57 (1903-1908), and Op. 58-74 (1910-1914). He made a gradual transition to atonality, beginning as early as 1903. It is precisely between the second and third periods when we begin to observe a significant shift taking place in Scriabin`s way of conceiving his music. The purpose of this paper is to document the decline of tritone in Scriabin`s music primarily found in the transitional part of the composer`s musical career. While the theory was formulated by Russian music theorists, it has had a direct influence on various ways of understanding Scriabin`s complicated later works. The second chapter deals with the tritone in Scriabin`s transitional period. The most important harmonic function in Scriabin`s transitional music is a ♭Ⅱ-Ⅴ progression. The third chapter explores Scriabin`s music from the viewpoint of Russian music theory. I focus primarily on the work of three Russian theorists, namely, Yavorsky, Dernova and Kholopov, and how their works are related to the tritone of Scriabin`s music. Both Dernova and Kholopov carry over Yavorsky`s theory when discussing Scriabin`s problematic compositions, and one gets the sense. The merit of Russian music theory lies in the methodology. In particular, Scriabin`s Poeme, Op. 59, No. 1 is examined by using Russian music theorists`s views. The Russian theorists offer a new system of analysis, thereby allowing us to have an intimate and perspicuous understanding of the late Scriabin`s mechanics.