Asynchronous circuits are crucial in designing low power and high performance digital systems. In this paper, we present an ecient modular partitioning approach for asynchronous circuit synthesis. This approach partitions a large circuit specication into smaller and manageablemodules that drastically reduces the synthesis complexity. Experimental results with a large number of practical asynchronous benchmarks are presented. They show that, compared to the existing techniques, this modular partitioning method achieves many orders of magnitude of performance improvement in terms of computing time, in addition to a reduced implementation area. It oers a practical solution for complex asynchronous circuit design problems.