The conference discussed regional cooperation and promoting the idea of social democracy, and a solidarity pact for the Western Balkans was signed.
PES chairman Poul Nyrup Rasmussen said that it was a pact for jobs, social justice and solidarity.
Zoran Milanovic, a member of the PES Presidency and a candidate for the president of the Social Democratic Party (SDP) of Croatia, said that he regarded the Democratic Party of Serbian President Boris Tadic as the SDP's partner because that party advocated the values championed by the PES.
"We see it as our partner, although it is less left than the traditional European Socialist mainstream. The party of (the assassinated prime minister) Zoran Djindjic, which is now led by Boris Tadic, champions the values of open society and we believe that it can lead Serbia forward," Milanovic said.
Milanovic said he was advocating "the socialism of the 21st century" in Croatia, because "there is no true democracy without the social democratic idea."
Addressing reporters, Luxembourg Foreign Minister Jean Asselborn said that Europe expected from Serbia a pro-European government that would fully cooperate with the Hague war crimes tribunal. He also said that Kosovo was a big challenge for Serbia and that the EU supported the plan proposed by UN mediator Martti Ahtisaari, which recommends supervised independence for the breakaway province.
The Kosovo issue is now before the UN Security Council and we all must respect what is decided there, Asselborn said.
PES chairman Rasmussen said that the PES would advocate the Western Balkans becoming a part of the European Union, and that he expected that the results of the new Serbian government would make it possible for Serbia to sign a Stabilisation and Association Agreement with the EU by the end of this year.
Serbian President Boris Tadic said he was pleased that the PES was actively supporting the integration of the Western Balkans and Serbia with the EU, stressing that it was the common political goal of the former Yugoslav republics and Albania to join the EU.
"I'm confident this great historic enterprise that lies ahead of us will be successful," Tadic said.