Disagreements about conservation and development in town centres of historic cities may emerge in a society because different interests have diverse wants in city conservation and development. If not reconciled, these can lead to unfavourable effects on historic towns/cities: urban development may threaten their special character and/or conservation restrictions may make town centres unattractive for investment. Observing these difficulties in the Thai historic cities, this research explores how the desires for conservation and development can be balanced in two historic towns in Ayutthaya, a World Heritage site in Thailand. Main points for discussions: 1) Conservation and development in historic town centres 2) Key concepts for balancing conservation with development including sustainability, viability and physical capacity. 3) The issues of conservation and development in Thailand, particularly in Ayutthaya. 4) A way to balance conservation and development in the case studies towns-Hua Ror and Chao Prom. The research confirms that city conservation is a public concern as well as a technical matter. This points to a significant role for stakeholders in increasing the acceptability and practicality of city conservation/development policy and its implementation.