Today’s high-speed network allows sophisticated applications of overlay networks. Meanwhile, usage of multicore processors has been spreading. The level of concurrency we need to handle has been rising rapidly, which necessitates a language that can express massive concurrency in a natural way, which can work with both tightly and loosely-coupled multiprocessor environments. This paper describes still work-in-progress design of “Overlay GHC”, an overlay network programming language based on concurrent logic language GHC (Guarded Horn Clauses)[10], as a candidate for such a language.