It appeared to be the biggest-ever seizure of counterfeit money in Cambodia, where dollars are commonly used for financial transactions.
Police Maj Song Sopheak said authorities had been tipped off and followed the men's car after it crossed the border into the northwestern province of Battambang. He said the fake banknotes had been packed in three boxes.
In October 2012, three Cambodian men were arrested for allegedly planning to smuggle millions of counterfeit dollars into Cambodia, reportedly in collusion with Thai businessmen.
Song Sopheak said the suspects are being held in the police station of Battambang's Phnom Proek district for questioning.
The men face a prison term of 5 to 10 years if convicted of trafficking counterfeit currency.