This paper proposes a multi-layered architecture of middleware for ubiquitous robots. Ubiquitous robots consist of different platforms with various functions and interfaces. Without a middleware, software agents have to hold information of all ubiquitous robots in advance to access other sensors or mobile robots. This decreases modularity and scalability of the entire system, therefore makes it difficult to develop and maintain software agents. The proposed architecture uses context information to decouple hardware and software agents as a bridge between them. Providing context-awareness to the middleware, software agents is able to get context information without accessing physical sensors directly, so that modularity and scalability are increased. Not only providing context information to software agents, the middleware uses mobile robots to gather as much sensor information as possible to generate context information actively. A middleware architecture is proposed with five layers classified due to device/environment dependencies, which are physical layer, device management layer, context provider and mobile robot(Mobot) scheduler layer, software robot(Sobot) management layer and software agent layer. The proposed middleware is implemented and simulated with virtual sensors in the virtual environment.