As a result of technological advance and ever-increasing stakeholder expectations, today’s engineering systems are becoming entities of a complex nature. Therefore, understanding and managing the complexity of such systems are becoming increasingly important, in particular during the early stages of the system development process, such as conceptual and preliminary design. In this paper, an analysis to measure the structural complexity of a system is presented. Systems with different architectural configurations (integral, linear-modular, and bus-modular) were analyzed at various levels of system decomposition. The results show that the structural complexity of a system depends largely on the architectural configurations at the lowest level of system decomposition. The sensitivities of each architectural configuration (due to the addition of more connections) were different. A real-life complex system was observed from the architectural configuration and structural complexity point of view.