Stuttering is a speech disorder which can be in the form of interruptions of speech, repetition of syllables, prolongation of syllables and repetition of incomplete phrases. This disorder can affect people's lives and their social and educational situations. Therefore, trying to understand its cause and its treatment is a necessary issue. However, discovering the causes of stuttering and the differences between people with stuttering and healthy people has always been a complex subject and despite extensive studies in this area, there is still no clear cause for this disorder. So this field needs more research. On the other hand, studying the chaotic characteristics of brain signals is a non-invasive method for testing brain function. This method can be used as a suitable method for studying brain wave patterns in stutterers and comparing them with healthy people and with this method, the differences in the electrical activity of the brains in the healthy people and stuttering people can be identified. The aim of this study was to investigate possible differences in the chaotic features of brain electrical activity in people who stutter compared to the healthy people by chaos theory to help diagnose the cause of stuttering. In this thesis, In order to compare the chaotic differences in electrical activity of the brain in stutterers and healthy people, 20 healthy subjects aged between 20 and 35 and 17 stuttering subjects aged between 20 and 35 participated and chaotic measurement, according to neuroscience adviser on 6 channels of EEG signals (F7, F8, T3, T4, T5 and T6) were measured. Before using chaotic analysis, sensitivity to the initial conditions, nonlinearity, and determinacy of the signals, which are the main features of chaotic signals, were tested. For this purpose, the Lyapunov exponent test and surrogate data test were used and the existence of chaos in the signals was proved. After that, the amount of chaos in the signals of two groups were initialized using four chaotic factor i.e. Lyapunov exponent, Hurst exponent, approximate entropy and sample entropy. Then the values obtained for the signals of the two groups were given to software for statistical comparison. The results of these four factors indicate that stuttering subjects has lower level of chaotic measures than control subjects and at the end, the hypothesis that stuttering is a functional disorder in the brain that may have been due to an abnormal activity (less than normal) in the areas of speech in the brain has been confirmed. Keywords: Stuttering, Chaos theory, Brain electrical activity, Surrogate data test