Service Orientation (SO) is a dominating technique evolving around the use of Object Orientation (OO). The conceptual comparison of both the approaches have been broadly explained in the literature, but the generalizable comparison of the maintainability of two paradigms is still a topic under research. This thesis tries to provide a generalized comparison of the maintainability using two functionally equivalent Online BookStore systems developed with Service Orientation and Object Orientation. This thesis presents a brief explanation of the software metrics used for the comparison. The quantitative comparison revealed that the Service-Oriented version of the system has a lower coupling and higher cohesion between software modules compared to an Object-Oriented approach. Through survey results, it was found that Service Orientation has a better degree of modifiability, encapsulation and abstraction while Object-Orientation provides a reduced degree of testing and system complexity comparatively. Also in expert interviews, participants believe that systems based on service orientation possess a better degree of stability, analyzability and modifiability whereas Object-Oriented System tends to provide a lower degree of structural complexity. Furthermore, experimental results suggest that a Service-Based System has a better degree of extensibility and changeability compared to Object-Oriented System.