The paper presents the study of the speech entrainment in dialogues of two interlocutors playing games. The calculations of the degree of speech entrainment are based on the acoustic characteristics of similar phonetic sequences. Formant values of stressed vowels in these words are considered. The recordings from the new SibLing corpus developed at the Department of Phonetics of St. Petersburg State University, were used as the material for the study. The results of the study confirmed the presence of speech entrainment in the values of the formants of stressed vowels. Based on the calculation of the Euclidean distance and the analysis of the vowel formant patterns, the following conclusions can be drawn: 1) In most cases, there is a mutual shift in the formant characteristics of vowels in the process of dialogue. 2) According to preliminary data, the degree of familiarity of the interlocutors quite strongly affects the speed of speech entrainment. The one case of divergence was observed. The degree of entrainment can be affected by the difference in age and social status. 3) The degree of adjustment of the acoustic characteristics depends on the quality of the vowel. To a greater extent, speakers adapt to each other by the rounded vowels of the back row (/o/, /u/), and also actively change the location of the vowels /a/ and /i/, adapting to each other. Moreover, the speakers often shift the focus of pronunciation of all cardinal vowels at once.