Dr. Ha's compositional style, up to this point in time of new millenium, may be divided into three periods. His early period reveals both tonal and atonal practice, while his maturing second period shows atonal practice only. The third period since 1990, almost exclusively, has been dedicated to writing music for church. His piano suite, DIABOLUS belongs to the first period written in dodecaphonic stlyle. However, it displays typical Baroque suite formet of four movements. The suite uses a tone row which is systemetically constructed in such a way that the second half of the tone row is the retrograde inversion of the first. The entire composion uses only four rows: O-0, O-6, R-0 and R-6. The four movements are as follows: Praeludium is in unipartite form. Menutto is in composite tripartite form. Sarabande is in simple tripartite form. Giga, which uses canonic imitation, is in composite tripartite form. It is noticeable, as is implied in the title, that the interval of tritone predominates throughout the work. The term "diabolus" is borrowed from the medieval expression which describes the difficulty of singing the augmented fourth interval, the devilish interval. The tone row is strictly used throughout except a few places where three, four and six-notes are used as a group. The use of tritones and note-groupings is outstanding, particularly, in Giga. The significance of this analytical study of Jae Eun Ha's composition lies in the fact that the first hand informations concerning not only the composition itself but also the composer himself may be obtained from the composer, who is still living and active, thereby leaving a valuable material to similar studies to come such as this. It is hoped that such analytical studies on Korean native composer's works may continue in the years to come so that future generations may benefit from enrichment of modern scholarship.