The drivers fled the scene, abandoning their vehicles, Udon Thani police chief Boonlue Kobangyang said.
The animals are believed to have been destined for China or Vietnam, via Laos. They will be returned to a nearby Thai national park where they are thought to have been captured.
Trade in pangolins is banned by the Convention on International Trade in Endangered Species (CITES).
The small mammals are nearly entirely covered with scales, made of keratin -- the same protein that makes up human hair. The scales are sought after in Vietnam and China as a remedy for allergies and to help male potency.