In view of the fact that the fashions and aspiration of each period are reflected in its buildings, this paper shows the importance of conserving monumental Yoruba traditional courtyard buildings, with Irefin Palace at Ibadan, Nigeria as a case study. It demystified the importance of Irefin Palace from different perspectives, as reasons for conserving it. With forces of modernization playing out in the twenty-first century, it becomes difficult to retain the original character of the building. This study identifies the historical importance of Irefin Palace in the context of social political structure of the ancient city of Ibadan and assesses the physical characteristics of the building in relation to method of construction, materials, structural members, spatial qualities as well as climatic comfort level. These were done through physical measurement of the building, oral interviews of the present occupants and some key informants, as well as general observation. Observations showed that Irefin Palace has undergone not a wanton or capricious change, but a form of metamorphosis or change of form by natural growth and development. The study concludes with practical proposals of conserving such a building in the midst of forces of modernization in the twenty-first century.