Dhaka, the capital city of Bangladesh, comprises of many mosques of Pre-Mughal (1204-1576 AD) and Mughal (1576-1751 AD) periods with great historical values and significance. Some of these historic mosques are now in the possession of the local people and the community of old Dhaka. These mosques are transforming due to the uncontrolled development by the community people in the name of modernization to accommodate their unlimited needs. The paper has termed these mosques as historic community mosques. These mosques represent a definite style of that period which is different from other mosque typologies in Bangladesh. The paper has discussed the historical significance of these mosques which possessed important architectural heritage. The paper has illustrated the gradual transformation of these historic mosques by the intervention of the community people through some case studies. It has also highlighted on how most of those historic testimonies of the past are losing the original architectural style and pattern, partially, and to some extent completely due to unplanned and uncontrolled development by the local people. These unplanned developments raise questions of authenticity of the historic past. Therefore, the authenticity of these structures will be verified through the comparison of the intrinsic pattern of mosque architecture built in Bengal during the Mughal and Pre-Mughal period and also from the information of researches done by the historians. . The paper focused on the aspect of participatory design processas an approach to attain more responsive design solutions and these transformed mosques are the vivid examples of such an approach. Those are viable examples of an interactive design process deeply rooted in local culture expressed through a live and endless process of design. Later, recommendations on conservation were given to protect these historic mosques from diminishing, so if they can be retained through the art of conservation, the past history and heritage may be cherished by the present and future generations.