They say that throughout 2010 more than 100 plants, 28 reptiles, 25 fish and seven amphibians were discovered.
But the WWF warns that many are endangered – while others could disappear before they are identified.
The Greater Mekong area includes Thailand, Cambodia, Burma, Vietnam, Laos and Yunnan province of China.
It is one of the world’s most bio-diverse areas, home to some of the planet’s most endangered wild species including the tiger, the Asian elephant and the Mekong dolphin.
The WWF says that more than 1,000 species have been discovered in the Greater Mekong over the past 10 years.
BBC environment reporter Mark Kinver says that new species are frequently found in the region because of increasing levels of human activity, which is proving to be a double-edged sword.
On the one hand, building roads opens up remote habitats to scientists who can then venture into previously unexplored areas and record the rich diversity of wildlife.
But this can also have a damaging ecological impact, especially if it results in a greater exploitation of the land which destroys these fragile ecosystems, our correspondent adds.
Among recent finds was a female-only lizard species, which reproduces by cloning, and was only discovered after a scientist spotted it on the menu of a Vietnamese restaurant.