As the increasing of system performance and computing power, embedded systems are more complicated and interactive. Therefore, operating system (OS) plays a more important role in embedded systems to utilize various hardware and software resources. However, no OS can meet all requirements of various embedded systems. Due to the advance of reconfigurable processors, system requirements can be more dynamic. Embedded OS has becoming more critical in the development of embedded systems and thus there is a strong need of configurable embedded OS to better and faster build up the target system. In this paper, we propose a configurable OS, called COS, based on SOA (Service-Oriented Architecture) for embedded SoC (System on a Chip) systems to build an application specific OS according to the system requirements. COS can be easily configured to better utilize the resources of the target embedded platform and have better support to the embedded application. Moreover, the COS can easily extend new features or functionalities of other OSes and even be adapted to the designs of other OSes. We implement COS on an ARM platform to prove its configurability and also evaluate its overhead. We believe that COS can be configured to meet the various requirements in embedded SoC systems and help to speed up the embedded system development process.