Bus Rapid Transit (BRT) systems have become a popular type of transportation in recent years thanks to travel comfort they present, travel time advantages and low investment costs compared with those of railway systems. BRT systems are used effectively in many parts of the world and showing a continuous increase in travel demand. BRT system in Turkey is currently applied only in Istanbul. This study focuses on the comparison of Istanbul BRT with some other BRT systems in developing countries. The BRT systems analysed through Data Envelopment Analysis (DEA) are those which have been evaluated and scored in terms of various criteria by ITDP. In other words, the BRT systems included in this study are those having BRT scores. Since most of the BRT systems are used in overcrowded cities, the inputs and outputs used in efficiency analysis have been specifically chosen from these cities. As a result of the findings, the study offers some improvement recommendations for the current BRT system in Istanbul and other BRTs in overcrowded cities. Besides being one of the three important outputs, BRT standard score is also a physical performance indicator and, therefore, this study provides a fairer and analytic comparison of different BRTs of developing countries.