The animal was spotted in a photo when a researcher, Hellat with the Annanba branch of the forest police bureau of Gansu was sorting pictures.
The photo was taken by a ranger named Junsibieke, or Jensbek (pronunciation), on March 4 from Gansu Province, state-run Xinhua news agency reported.
The Annanba wild camel national nature reserve was founded in 2006. "This is the first time we have found the snow leopard here. It is such a pity that we didn't see the photo until today," said Hellat.
Junsibieke recalled that the leopard was an adult about 1.5 metres long. It had a blood stain on its face.
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Snow leopards, one of China's Class A protected animals, are usually found in the Himalayan ranges of central and south Asia at altitudes between 3,000 and 5,500 metres.
The animal has rarely been seen in the wild since last century due to loss of habitat and poaching.
An estimated 3,500 to 7,000 snow leopards live in the wild, in addition to 600 to 700 more in zoos worldwide.
"That snow leopard must be following them", he said.
Located at the junction of the provinces of Gansu and Qinghai and Xinjiang Uygur Autonomous Region, the Annanba nature reserve covers 39.6 hectares and has an average altitude of about 2,000 meters.
Other rare animals such as the Lynx and Manul also live in the reserve.