The Vietnam Automobile Manufacturers Association (VAMA) saw 17,314 units sold, down 51% from December.
Hyundai Thanh Cong, which assembles and distributes cars for the South Korean brand Hyundai, sold 64% less from the previous month, while VinFast saw sales dip 92%.
The combined sales of VAMA and the two brands mentioned dropped 57% from December to 21,168 units.
Industry insiders say that as customers tend to buy new cars in the month before Tet, the biggest annual holiday which fell on Jan. 20-26 this year, it is understandable why sales surged in December and dropped in January.
Declines were seen even among the best-selling models.
Toyota Vios sales dropped 90% from December, while that of SUV Mazda CX-5 fell 42%.
Since early February dealers have been offering discounts of up to VND100 million ($4,200) to boost sales.