Hatidza Mehmedovic, who headed the Mothers of Srebrenica association following the 1995 massacre, has died aged 65.
The Srebrenica Islamic Community said Mrs Mehmedovic died on Sunday.
Bosnian media said she was in a Sarajevo hospital.
Mrs Mehmedovic’s husband, two sons and brother were among some 8,000 Muslim men and boys from Srebrenica who were killed when Bosnian Serb troops overran the eastern enclave in July 1995.
The massacre is considered Europe’s worst since the Second World War.
The Mothers of Srebrenica group has fought for those responsible for the killings to be brought to justice.
The UN war crimes tribunal for the former Yugoslavia has sentenced Bosnian Serb wartime leader Radovan Karadzic and his military commander Ratko Mladic over the Srebrenica massacre and other atrocities during the 1992-95 war.