The remains of 200 defenders and civilians, taken from Vukovar's hospital, were exhumed at that farm in 1996.
Milanovic was accompanied by First Deputy PM Vesna Pusic, many ministers, and Vukovar Mayor Zeljko Sabo.
Before that, a government delegation led by Milanovic laid a wreath and lit a candle at the Homeland War Victims Memorial Cemetery in Vukovar, paying respects to the town's residents killed in the 1991 military aggression. The delegation also walked in a procession of remembrance from the hospital to the cemetery.
Over 50,000 people from all over Croatia attended today's commemoration.
According to the 2011 census, Vukovar has a population of 28,000.