This paper investigates the decentralized robust output tracking problem for a class of linear uncertain interconnected systems. The uncertainties are assumed to be time-invariant and satisfy the matching conditions for each decomposed subsystem. By modifying the control law for the optimal solution of each nominal augmented subsystem, the overall uncertain interconnected system can approach the constant reference output with a prescribed convergent rate. This method is very simple and effective, and can reject any constant but unknown disturbances imposed on the states. A demonstrative example is also given.