The animals, weighing a total 600 kilograms, were found at three locations in Ha Tinh Province’s Huong Son District by officers from the Ministry of Public Security and the local police department.
They also found an item weighing a kilogram that they suspect is ivory.
The five women and four men in custody are all locals and the police are investigating further.
Pangolin trafficking is not rare in Vietnam, where it is legally protected and categorized as endangered.
The shy, tiny creature, which resembles a scaly anteater, is the world's most heavily trafficked mammal despite bans. Pangolins are hunted in Vietnam and its neighborhood for their meat and the alleged medicinal properties of their scales.
Of the 10 countries and territories with the largest number of trafficking incidents, seven were in Asia -- China, Vietnam, Malaysia, Hong Kong, Thailand, Laos, and Indonesia – a study by wildlife trade monitoring group Traffic and Australia’s University of Adelaide in December 2017 had found.