Urban sustainability has become a significant challenge globally due to rapidly growing urbanization and industrialization. Hence, this study was conducted to examine the existing urban development trends of metropolitan cities (i.e., Beijing and Karachi) of China and Pakistan in the context of urban sustainability. The development progress in both cities was examined through urban sustainability indices individually and compared with each other. An index system considering 36 indicators was developed based on social, economic, and environmental aspects. The six years (2012–2017) of data used in this study, were obtained from various governmental websites. Furthermore, the Urban Sustainability Index (USI) was evaluated using the statistical standard equal-weighted method. Results revealed that Beijing’s developmental progress is much better than Karachi in terms of socio-economic and environmental development, but there is still a need for improvement. While Karachi faces problems in all three sectors, each indicator of these sectors requires considerable improvement for attaining the top level of the Urban Sustainability Index. However, this study recommends that much attention is needed in the case of Karachi city, whereas Beijing also needs quality advancement in urban development.