One of the consequences of defenseless spaces in cities is a decrease in security and more importantly, a decrease in the sense of security among citizens. Therefore, it is necessary to investigate these spaces and evaluate their effects on citizens' sense of security. In this regard, the purpose of this research is to investigate the impact of defenseless spaces on the sense of safety of citizens in Tehran's Bazar neighborhood. This research is applied in terms of purpose and in terms of documentary-field (questionnaire) method. Three indicators (physical, social and socio-physical) and three indicators (linguistic, physical and visual sense of security) have been used to investigate defenseless spaces. Using Cochran's formula, the sample size is 384 according to the statistical population (23,696 people). SPSS and SMART-PLS software were used for data analysis. The results of the research have shown that there is a significant relationship between the physical and social index and the sense of security of the citizens, but there is no significant relationship between the social-physical index and the sense of security. Also, the social index (crowdedness, solitude, etc.) has the greatest impact on citizens' sense of security.