Statement of the problem. The relevance of the research topic is related to the need for a comprehensive study of Jörg Widmann’s musical creative work, in particular in the aspects of compositional and performing activities and an indepth performing analysis of his Fantasy for solo clarinet. Analysis of recent research and publications. The study is based on the works that examine the creativity of composers of the 20th century (Gromchenko, Vovk, Metlushko, Odom, Rehfeldt, Teixeira); the creative work of J. Widmann (Bruhn, Besthorn, Reyes, Dierickx); of the fantasy genre (Nikolaievska & others), as well as an interview with the composer (Wollenweber; Wilsom, Fein, Christopher). The main objective of the study is to perform a performing analysis of the selected composition in terms of mutual influences of the artist’s compositional and performing styles. The scientific novelty is related to the formation of the author’s algorithm of the performing analysis and its application to the selected composition based on one’s own interpretation. The author’s algorithm includes such stages as intellectual, technological and synergistic, which allows one to fully understand the genre and style concept of the composition and the way of its implementation. Research methodology is based on an analytical approach (performing analysis), genre, style and system approaches are also involved. Results. The intellectual stage of the performing analysis made it possible to find genre principles and their individual manifestation in J. Widmann’s creativity. The manifestation of intertextuality is marked by constant allusions to the famous compositions by C. M. Weber, J. Brahms, R. Schumann, K. Stockhausen, I. Stravinsky or instrumental compositions; performance influence – through the manifestation of the improvisational nature of performing thinking (in particular regarding the metrorhythmic organization of Fantasy) and the concert nature of the compositions, which led to the choice of means of expression, themes, tempos, theatricality, and the effectiveness of the opus. The form of Fantasy is defined as a contrastive-composition, the importance of a harmonious solution is emphasized. The technological stage of the performing analysis touches upon the issues of the instrument, technological features of performance (multiphonics, playing in the lowest register of the clarinet in the nuance of ppp, creating a loud noise from the valves of the instrument, clicking keys, working with a fast tempo, contrasting dynamics, double-tongue technique for playing sixteenths, etc.). Conclusions contain a synergistic stage of performing analysis. Thus, it is indicated that Fantasy presents the development of certain features that consistently characterize the compositional and performing style of J. Widmann. Emphasis is placed on the organic combination of composing and performing in the creative work of J. Widmann and the significant influence of the performer’s sense of time and space on the creation of his compositions, it is indicated that the parity of both types of creativity determines their mutual enrichment. Such features of the composer’s creativity as the synthesis of tradition/ innovation, intertextuality, concert performance, intellectualism, the diversity of the composer’s legacy and the breadth in the involvement of instruments, styles, and themes are singled out as well as the manifestation of the improvisational nature of performing thinking, the influence of the performing time-space feeling on the creation of compositions. We have named the following features of J. Widmann’s performing style: virtuosity, thorough approach to ease of performance; inquisitiveness, working with different timbres, attention to dynamics and tempos; awareness of harmony as the foundation of the organization of the composition; working with sound, feeling its plasticity, living breath, overtone colours; intellectualism of performance, which is manifested in a clear idea of the structure of the composition, accentuation of caesuras, other punctuation marks of performing formation.