Ukraine's tendency to achieve compatibility with the standards of NATO member states, in particular as a result of Russian aggression against Ukraine, raises the issue of developing the diagnostic competence of foreign language teachers in higher military educational institutions. After all, the ability of foreign language teachers in higher military educational institutions to effectively assess the levels of foreign language communicative competence of military personnel allows them to respond promptly to problematic issues in their language training and change training strategies following the needs of the Armed Forces. Therefore, the study aims to reveal the essence of the methodology of adaptive development of foreign language teachers' diagnostic competence in the system of postgraduate education. To achieve this goal, several theoretical (analysis, synthesis, systematisation of scientific psychological, pedagogical, methodological literature) and empirical (observation, comparison, description) methods were used. Adaptive learning technologies are proposed, which allow studying the educational material with the help of adaptive algorithms for each student, according to knowledge, skills, and personal learning needs, i.e., through the adaptive presentation of the educational material of the author's remote special course. The stages of implementation of the author's methodology for adaptive development of diagnostic competence of foreign language teachers in higher military educational institutions are highlighted. The specifics of the methodology of adaptive development of diagnostic competence of foreign language teachers are revealed, considering their diagnostic activities in the system of military education. The authors' developed methodology for the adaptive development of diagnostic competence of foreign language teachers in higher military educational institutions contributes to the actualisation, systematisation and deepening of their theoretical diagnostic knowledge, and improvement of practical diagnostic skills and abilities that form the basis for the development of their diagnostic competence. The practical significance of the study lies in the possibility of applying its results to improve the qualifications of foreign language teachers at higher military educational institutions