The International Rescue Committee (IRC),which carried out the study with Australia's Burnet Institute,said Democratic Republic of Congo's 1998-2003 war and its aftermath had caused more deaths than any other conflict since World War II.
"Congo's loss is equivalent to the entire population of Denmark or the state of Colorado perishing within a decade,"George Rupp,president of the aid group,said in a statement.
The findings were published on the day Congo's government and warring eastern rebel and militia factions were due to sign a ceasefire in the hope of halting fighting in the east which has raged on since the nominal end of the 1998-2003 war.
Rupp said that although Congo's war formally ended five years ago,"ongoing strife and poverty continue to take a staggering toll"."The conflict and its aftermath,in terms of fatalities,surpass any other since World War II,"he added.
Malaria,diarrhoea,pneumonia and malnutrition,aggravated by conflict,were the top killers in Congo,the survey said.
"Most of the deaths are due to easily treatable and preventable diseases through the collapse of health systems and the disruption of livelihoods,"said IRC director of global health programs Richard Brennan,one of the survey's authors.
Congo has the lowest spending on health care of any country in the world at an average of just $US15 ($A17.46) per person per year.
"If you're in the United States,we spend $US6000 per person per year,"Brennan said.
The study was conducted between January 2006 and April 2007 in 14,000 households in all the country's 11 provinces. It updated previous surveys which estimated the toll from Congo's war at around four million.
The IRC said an estimated 727,000 people died in excess of normal mortality during the latest survey period. Children under the age of five were the hardest hit,accounting for nearly half of all deaths despite making up 19 per cent of the population.
Before the latest survey,humanitarian workers had estimated that more than 1,000 people a day were dying in Congo.
"Since our last study in 2004,there's been no change in the national rate,which is nearly 60 per cent higher than the sub-Saharan average,"Brennan said.
But in the east,where rebel groups,local militia,and Congo's own army prey on civilians with impunity,the mortality rate is 85 per cent higher than the sub-Saharan African average.
The vast former Belgian colony's 1998-2003 war sucked in its neighbours,as foreign armies and rebel groups vied for control of the country's rich natural resources. The conflict wrecked infrastructure already weakened by decades of neglect and corrupt leadership and forced millions to flee their homes.
A 2003 peace agreement led to the formation of a transitional government and multi-party elections were held in 2006,won by President Joseph Kabila.
Rupp said he hoped the peace deal for the east,due to be signed on Tuesday by the government,Tutsi rebels and Mai Mai militias,could finally draw a line under Congo's crisis.
"We hope this week's peace agreement in North Kivu will mean an end to the hostilities and a restart of reconciliation and recovery efforts,"he said.
The IRC called for security reforms,increased spending on basic services like health care and continued support for the 17,000-strong United Nations peacekeeping mission in Congo.
Reuters