balancing development with conservation is a matter of long-running debate within the domain of urban literature, Since the beginning of the modern movement, different theories have been developed on urban conservation and development, Concomitantly, a broad spectrum of approaches have emerged to relief this challenge, One underlying trend is based on the conflict between conservation and development, From this perspective, within the context of a city a dichotomy exists between the conservation of the old parts and the need for development, Two controversial points of view get involved in this school of thought, From the first point of view, development is the necessity, while conservation is considered as a great and insurmountable barrier to urban development; from the other viewpoint the primary concern is conservation, addressing the worrying trend of urban development toward removing the cultural and traditional values from our living environment, However more recently a new and balanced approach is adopted, emphasizing on the integration of urban conservation and development as a prerequisite for the survival of a city, yet it has not represented practical solutions to the issue. City as a living environment is subjected to development, thus effective and workable solutions to meet the challenge between development and conservation can be provided by considering a well-tested model of development in terms of the interaction between conservation measures and development strategies, A well- experimented and effective development model, concerning conservation, is going to be analyzed, as a case study, with reference to the historic city of Yazd with its long-term survival from 11 to 19 century, An interpretive-historical method has been adopted, Data were collected by field observation and literature review, then discussed thorough logical argument, From this scrutinizing study, the conservation characteristics of Yazd development model have emerged. Six main steps could be recognized in Yazd physical development model, from 11 to 19 century, occurring in the inner and outer parts of the city, The model involves four intervention categories: 1- Preservation and restoration of the old buildings, 2- Rehabilitation of the old fabric, 3- Construction of new buildings in the inner part, and 4, New attachments to the city in the outer part, The first 3 steps are in direct relationship with the concept of conservation as an operation to prolong the life of the city, In fact, These interventions turn the challenges to interaction opportunities. Based on the adopted developmental measures, the main and distinguishing characteristics of Yazd development model have been revealed as follows: 1- Enhancing the active role of the old part, 2- Providing an essential change opportunity, 3- Decreasing the extra loads on the old part, 4- Centrality of the old part in the city development, and 5- Creating a relationship between the old and new part, Yazd development model can be considered as a conservation-oriented development, In this development model, conservation is adopted as the main and effective development strategy, which not only contributes largely to upgrading environmental quality and physical improvement but also serves as a fundamental catalyst for change.