The report, which was released on Friday, also said that HIV infections could soar to 90 million - or more than 10% of the continent's population - if more is not done soon to fight the disease.
More than 25 million Africans have been infected with HIV, the virus that causes Aids.
Unaids, a UN agency set up to address problems of HIV-Aids, estimates that nearly $200 billion is needed to save 16 million people from death and 43 million people from becoming infected, but donors have pledged nowhere near that amount.
In its report Aids in Africa, the UN agency examines three potential scenarios for the continent in the next 20 years depending on the international community's contribution to fighting the epidemic.
Researchers determined that even with massive funding and better treatment, the number of Africans who will die from the virus is likely to top 67 million.
"What we do today will change the future," concluded the report, which was drawn up by hundreds of the world's leading experts on HIV and Aids as well as people living with the virus.
"These scenarios demonstrate that, while societies will have to deal with Aids for some time to come, the extent of the epidemic's impact will depend on the responses and investment now."
The three scenarios include a best-case situation, a middle case and a doomsday scenario. They all warn that the worst of the epidemic's impact is still to come.
"The scenarios are not predictions, they are plausible stories about the future," Unaids chief Dr Peter Piot said. "The scenarios highlight the various choices that are likely to confront African countries in the coming decades."
"There is no single policy prescription that will change the outcome of the epidemic," the report stated. "The death toll will continue to rise no matter what is done."
In 2004, 3.1 million people were
infected with Aids
Under the worst-case scenario, experts have plotted current policies and funding over the next two decades.
"It offers a disturbing window on the future death toll across the continent, with the cumulative number of people dying from Aids increasing more than fourfold," it says.
"The number of children orphaned by the epidemic will continue to rise beyond 2025."
Aids already has a devastating impact on the continent. Unaids has reported that life expectancy in nine countries has dropped to below 40 because of the disease. There are 11 million orphans, while 6500 people are dying every day.
In 2004, 3.1 million people were newly infected, the agency said. "If by 2025 millions of African people are still becoming infected with HIV each year, these scenarios suggest that it will not be because there was no choice," the report said.
"It will be because, collectively, there was insufficient political will to change behaviour at all levels from the institution, to the community, to the individual and halt the forces driving the Aids epidemic in Africa."
Unaids' Piot said there was hope. "Millions of new infections can be prevented if Africa and the rest of the world decide to tackle Aids as an exceptional crisis that has the potential to devastate entire societies and economies."