The South China Sea is a common resource where ASEAN Member States derive multiple uses. Nevertheless, the competing claims and conflicting interests of ASEAN nations and other claimants, such as China, raise the issue of transboundary harm within this sea and the sustainability of its resources. This paper argues that, despite the absence of a region-based transboundary environmental impact assessment [EIA] regime covering the South China Sea, ASEAN Member States are bound by their commitments under the Law of the Sea Convention and other binding agreements, as complemented by customary international law, which provide guidance in applying a transboundary EIA over a shared resource. The South China Sea Arbitration particularly sets the minimum requisites of not only preparing an EIA, but also communicating the EIA results to relevant international organizations. Here, ASEAN can play a vital role as a platform through which where EIA communication can be channelled.