Introduction. Accompanying high school students in the process of professional self-determination is an urgent task for the main subjects of vocational guidance − schools and universities. The article reveals the specifics of cooperation between the rural lyceum and the key university in the organization of professional orientation of students in grades 8−11. The purpose of the article is to summarize theoretical research and the results of practi-cal experience of joint work of the Mari State University and the Korkatovsky Lyceum of the Republic of Mari El to support the professional choice of high school students. Materials and methods. The material for the study was the program documents of the last decade on the issues of professional self-determination of students: the National Project “Education” (2018), the Concepts of supporting professional self-determination of students in the conditions of continuity of education, developed by the Center of the FSAU “FIROˮ 2012, 2015). Three main groups of methods were used in the work: theoretical analysis of scientific and pedagogical literature on the problems of the article, modeling, study and generalization of best practices in the management of educa-tional systems. The result of the research was the development of the theory of support of professional choice of school graduates; improvement of the methodology of support of professional choice of school graduates based on the model of systematic career guidance work with schoolchildren, the main directions of which are: profes-sional information, self-determination training, practice-oriented support of professional choice; proper orienta-tion in the world of modern professions and a conscious choice of vocational and educational trajectory by stu-dents of senior classes of the lyceum, depending on their interests, abilities, vocation, opportunities, personal characteristics, health status, and the like. The discussion confirmed: the importance of supporting the profes-sional choice of school graduates based on the model of systematic career guidance, the practical orientation of methodological innovations in career guidance carried out in cooperation between the key university and the rural lyceum to support the professional choice of students; the significance of the experience gained for the practice of cooperation between secondary educational organizations and organizations of higher professional education in supporting students. Conclusion. The long-term practical experience in supporting the profession-al choice of high school students in the conditions of cooperation between the lyceum and the key university is summarized, methodological approaches to the organization of career guidance are defined, conclusions are drawn on the effectiveness of the development of work on comprehensive support of professional choice and as-sistance in building a career trajectory.