The activity of supplementary education system employee is associated with the syncretic pedagogical and creative process organization with students, their parents and various social partners participation. The circumstances in which supplementary education teacher finds himself often turn out to be unforeseen and require spontaneous effective actions from him ‒ professional improvisation. It becomes more productive with the expected understanding of its prerequisites, conditions and results. In this regard, the purpose of this article was the theoretical and methodological substantiation of the potential of reflexive pedagogy use in supplementary education teachers professional improvisation culture development. Within the framework of the described study, conducted on Donetsk Republican Institute for the Education Development basis, the reflective pedagogy possibilities were studied as part of the supplementary education teachers professional improvisation culture formation in the postgraduate education system. The experiment involved the inclusion of the module Supplementary education teachers professional improvisation culture in the additional professional program for supplementary education teachers, which included a section using the reflective pedagogy potential. The practices offered to teachers involved improvised professional actions assessment with their subsequent discussion. As a result, the personal reflexive skills structure and content within the framework of the supplementary education teachers professional improvisation culture were described, and their development methodology for was proposed. The practical significance of the study is confirmed by the professional and personal results diagnostics data of additional professional program mastering, in connection with which the author considers promising further research in the field of reflective practices use in the supplementary education teachers postgraduate education system.