The Austro-Serbian Convention of 1881 was a secret bilateral treaty that was signed in Belgrade on 28 June 1881 by Gabriel Freiherr Herbert-Rathkeal on behalf of Austria-Hungary and by Čedomilj Mijatović on behalf of the Principality of Serbia. The convention effectively turned Serbia into a protectorate state of Austria-Hungary, which meant its accession by proxy to the subsequent Triple Alliance (1882). Serbia then received Austrian support during the Serbo-Bulgarian War.