Officials said talks would start during the Irish presidency, which begins Jan. 1 and runs through June 30, the Belgrade radio station B92 reported.
Swedish Foreign Minister Carl Bildt told reporters in Brussels he could not give them a specific date.
"This is not about a date, but about a timetable," he said.
The most difficult issue is Serbia's withdrawal of troops from northern Kosovo. A majority of the residents in the region are ethnically Serb.
The union may also hold talks with Kosovo. Spain and four other EU members have not recognized Kosovo and are skeptical about its membership.