The document, whose content covers traditional Tibetan medicine and religion, was found at the monastery in Nyemo county on the outskirts of Lhasa last week, Tashi Gyatso, an official with Tibetan capital's cultural bureau said.
"The pages were loose and the document was incomplete...But the text, written in black ink and on quality Tibetan paper made of bark fiber, was still legible," he said.
Though the text was written in Tibetan, most of the pages were numbered with Chinese characters, the official said.
The document was compiled during the Yuan Dynasty (1271-1368), almost 800 years ago, state-run Xinhua news agency quoted Pempa Tsering, a Lhasa-based specialist on ancient Tibetan literature as saying.
Tashi Gyatso said the local cultural authorities are preparing to include the rare document on China's national list of endangered cultural heritage for special preservation.
"The finding was among a total of 853 cultural heritage pieces uncovered in Lhasa over the past year," he said.
"The cultural bureau is making a list of the city's cultural heritage items between 2011 and 2015, in order to better preserve these valuables," he said.