Background: The aim of the present study was to investigate the mediating role of defense mechanisms in the relationship between behavioral brain systems and Alexithymia in students of Sari Farhangian University.  
Method: The statistical population of this study was all students of Farhangian University of Sari in the academic year of 2018-2019. From this statistical population, a sample of 234 people was selected by stratified random method.  To measure the research variables, the Defense Mechanisms Questionnaire (DSQ) questionnaire, Carver and White Behavioral Activation and Activation Systems Questionnaire and Alexithymia Questionnaire were used. The proposed model was evaluated using structural equation modeling.
Results: In general, the results showed that brain-behavioral systems and defense mechanisms have a direct role in Alexithymia(p­<0/01). Behavioral activation system and developed defense mechanism showed a negative and significant effect on alexithymia and behavioral inhibition system and defense mechanisms (undeveloped and neuroticism defense styles) showed a positive and significant effect on emotional malaise.Also, brain-behavioral systems with the mediating role of defense mechanisms indirectly played a role in Alexithymia(p­<0/01). Therefore the results showed that the proposed model of causal relationships between these variables had an acceptable fit.