The commissioner also stressed the importance of meeting obligations towards the International Criminal Tribunal for the former Yugoslavia (ICTY).
The European Union will finally open its door to Croatia after the country realises full cooperation with the ICTY, Rehn said in an interview for Television Bosnia-Herzegovina on Monday evening.
Answering to a reporter's question what would happen should Croatia fail to extradite fugitive general Ante Gotovina to the ICTY by spring, Rehn said he was confident Croatia would do its best to meet that obligation.
He expressed hope Croatia would locate Gotovina and extradite him to the Hague tribunal.
The EU commissioner was on a two-day visit to Bosnia where he spoke to Bosnian officials on the importance of cooperation with the ICTY and the new organisation of police forces in Bosnia.