This paper examines how China has played a "responsible" role in international humanitarian post-disaster assistance by taking the example of China’s assistance to post-tsunami Aceh,and explores policy implications with regard to future Sino-Australian security cooperation.China and Australia took inconsistent approaches to assistance in Aceh,which derived from their different understandings of international "responsibility".However,the inconsistencies do not necessarily hamper cooperation between the two.Rather,it is because of these inconsistent approaches that the two countries’ cooperation can develop into comprehensive and multifaceted assistance.The key to successful cooperation between the two countries,this paper argues,is the notion of "complementarity".In policy documents on bilateral relations,Chinese and Australian policymakers emphasize the "economic complementarity" between the two,but this "complementarity" is also useful when the two explore the way in which they will cooperate on security issues.One example of this complementary approach with regard to assistance for Aceh is the Australian effort to promote stability in both tsunami and non-tsunami affected areas,and Chinese economic investment in Aceh,in keeping with the Acehnese local expectations of long-term economic development and more employment opportunities,which are the foundation stones of stability.While these efforts are not consistent,they are highly complementary to each other,and have great potential to encourage peace and stability in Aceh.