The report, entitled Antarctic Penguins and Climate Change, was read out at a UN international climate change conference in Bali, Indonesia.
It said that the rapid melting of ice in Antarctica was killing the habitual habitat of penguins as well as reducing their food resources.
A WWF Web site, www.panda.org, said the report "shows that the four populations of penguins that breed on the Antarctic continent - Adelie, Emperor, Chinstrap and Gentoo - are under escalating pressure."
"In the northwestern coast of the Antarctic Peninsula, where warming has been the most dramatic, populations of Adelie penguins have dropped by 65% over the past 25 years," the Web site said.
"The Antarctic penguins already have a long march behind them," the site quoted Anna Reynolds, Deputy Director of WWF's Global Climate Change Program, as saying. "Now it seems these icons of the Antarctic will have to face an extremely tough battle to adapt to the unprecedented rate of climate change."
UN Secretary General Ban Ki-moon, who visited Antarctica on November 10, said he was concerned about the melting of glaciers and pledged to take measures.
According to the WWF Web site, the Antarctic Peninsula is warming five times faster than the average rate of global warming.