The Malaysian drug trafficking suspects said they bought the drugs for two million baht from a Thai northern town.
They said the drug could fetch up to four million baht a kilogramme in Malaysia.
They said they were only couriers and were paid only 25,000 baht a kilogramme to take them back across the border.
According to JS 100 Radio, the seizure of the huge cache and the Malaysian gang followed the arrest of nine other Malaysian suspects in Hat Yai, and other southern towns.
Investigation and confession by these suspects led narcotics suppression police to plan the arrest of other accomplices who would return to Malaysia on the Bangkok-Butterworth train with the drugs.
The drugs seized on board the train last night were wrapped in a small pack of one-kilogramme each, totalling 75 packages.
All the suspects were being brought to Bangkok for a press conference, expected today.