Gorillas, orangutans, and corals are among the plants and animals which are sliding closer to extinction.
The Red List of Threatened Species for 2007 names habitat loss, hunting and climate change among the causes.
The World Conservation Union (IUCN) has identified more than 16,000 species threatened with extinction, while prospects have brightened for only one.
The IUCN says there is a lack of political will to tackle the global erosion of nature.
Governments have pledged to stem the loss of species by 2010; but it does not appear to be happening.
“This year’s Red List shows that the invaluable efforts made so far to protect species are not enough,” said the organisation’s director-general, Julia Marton-Lefevre.
“The rate of biodiversity loss is increasing, and we need to act now to significantly reduce it and stave off this global extinction crisis.”
One in three amphibians, one in four mammals, one in eight birds and 70% of plants so far assessed are believed to be at risk of extinction, with human alteration of their habitat the single biggest cause.