Urban security is considered one of the key indicators of sustainable urban development, especially in neighborhoods with contrasting physical and social characteristics. This research aims to assess and compare the sense of security in the old and new urban fabric of Chelleh Khaneh Neighborhood in Rasht, based on the principles of Crime Prevention Through Environmental Design (CPTED). The objective of this study is to conduct a comparative analysis of the level of security within the physical environment of the Chelleh Khaneh neighborhood in Rasht. This applied research employs a mixed-methods approach (both quantitative and qualitative), including field observations and spatial analysis in both parts of the neighborhood. The comparative analysis uses CPTED indicators to evaluate the physical features that influence the sense of security. The research question is: How have the principles of CPTED manifested in the old and new fabric of Chelleh Khaneh, and how do these differences affect residents' perception of security? The findings show that, despite organic spatial patterns and limited natural surveillance, the old fabric has higher social cohesion and more informal surveillance. In contrast, the new fabric benefits from better physical design elements, such as lighting and access control, but the lack of a sense of belonging and social ties negatively impacts residents' security perceptions. Key CPTED indicators, such as natural surveillance and territorial reinforcement, have shown different performances in these two urban fabrics. The innovation of this study lies in the integrated evaluation of CPTED principles within two different morphological contexts in a single neighborhood, providing practical insights for urban designers and policymakers to enhance urban security in both traditional and modern urban fabrics.