A camera trap captured this image of the endangered Saola.
The Saola, a long-horned ox, was photographed by a camera in a forest in central Vietnam in September, the WWF said in a statement Wednesday.
"This is a breathtaking discovery and renews hope for the recovery of the species," Van Ngoc Thinh, WWF - Vietnam's country director, was quoted as saying.
The animal was discovered in the remote areas of high mountains near the border with Laos in 1992 when a joint team of WWF and Vietnam's forest control agency found a skull with unusual horns in a hunter's home. The find proved to be the first large mammal new to science in more than 50 years, according to the WWF.
In Vietnam, the last sighting of a Saola in the wild was in 1998, according to Dang Dinh Nguyen, director of the Saola natural reserve in central province of Quang Nam.
In the area where the Saola was photographed, WWF has recruited forest guards from local communities to remove snares and battle illegal hunting, the greatest threat to Saola's survival, the statement said. The snares were set to largely catch other animals, such as deer and civets, which are a delicacy in Vietnam.
Twenty years after its discovery, little is known about Saola and the difficulty in detecting the elusive animal has prevented scientists from making a precise population estimate.
At best, no more than few hundreds, and maybe only a few dozen, survive the remote, dense forests along the border with Laos, WWF said