Urban vitality is widely recognized as an authentic philosophy that reflects chaotic urbanization and orthodox planning in the developed world. However, comparative studies on the urban vitality of developing countries are scarce. This study developed a framework for analyzing urban vitality in developing countries. Using Ho Chi Minh City and Shanghai as cases, we measured urban vitality and analyzed its spatial pattern by using a projection pursuit model based on three dimensions of human activity, built environment, and their linkage. Both cities show a declining gradient of urban vitality from the urban cores to suburbs. However, Shanghai also fosters several peaks of urban vitality in its subcenters. The different spatial patterns of urban vitality are largely determined by the monocentric or polycentric urban form. A similar pattern of high urban vitality in both urban cores may be associated with the European-style block planning in the former concession areas. Recently, these two cities launched large-scale transport projects and replicated the modern style of broad and grid roads from the US, thereby reducing their urban vitality. This comparative study can improve our understanding of urban vitality patterns in developing countries and provide some planning suggestions that can help nurture urban vitality.