A total of six million pills of the drug known as Captagon were found inside two refrigerated lorries.
It was one of the largest such hauls ever intercepted, the Jordanian Customs Department said.
Captagon, dubbed "the poor man's cocaine", is produced in huge quantities in Syria, which a decade-long war has turned into a narco-state.
At the height of the conflict militant groups supplied the drug to fighters - which is often laced with caffeine - to boost their courage.
With growing poverty, many ordinary Syrians became involved in the trade, which is now worth far more than any legal exports.
The amphetamine is smuggled into neighbouring countries, such as Jordan and Lebanon. The final destination is often in Gulf states where there is a big market.
The latest seizure was made at the Al-Karamah border crossing between Iraq and Jordan.
Details are sketchy. It is unclear where the pills were to be sold or how many arrests were made.
A 2021 report by a Cyprus-based think tank said Captagon production had a market value of about $3.5bn (£2.7bn; €3.2bn) in the previous year.
Skirmishes between the Jordanian military and drug traffickers are becoming more frequent, with larger hauls being made.
Soldiers have a shoot-to-kill policy. Last January 27 traffickers were killed as the Jordanian army foiled a co-ordinated effort to cross into the country.