The paper investigates the factors of professional deformation of the personality of a high school teacher. The attention is paid to the increased requirements of the dynamics of global processes taking place in the modern educational space, to the personality and activities of the teacher. Observations show that the daily performance of teachers' professional duties over many years shapes habits, mindsets, and communication styles, and the individual acquires certain traits that can be considered disharmony. It was found that professional deformation is manifested in changes in the parameters of the personal characteristics of the teacher, which ultimately causes a change in functioning. Based on the theoretical analysis, the internal factors that determine the manifestation of professional deformation of the teacher's personality are identified. We analyze the most significant personal manifestations such as conservatism, rigidity, dogmatism, conformism, stereotyped thinking, lack of motivation, and frustration. The findings of this study support the idea that these factors can block the teacher's willingness to reconsider views, and cause the preservation of experience, which leads to professional deformation of personality. [ABSTRACT FROM AUTHOR]