Saudi prince Abdel Mohsen Bin Walid Bin Abdulaziz and four others were detained by airport security while allegedly "attempting to smuggle about two tons of Captagon pills and some cocaine," a security source told AFP.
"The smuggling operation is the largest one that has been foiled through the Beirut International Airport," the source said on condition of anonymity.
Captagon is the brand name for the amphetamine phenethylline, a synthetic stimulant. The banned drug is consumed mainly in the Middle East and has reportedly been widely used by fighters in Syria.
The five Saudi citizens were still in the airport and would be questioned by Lebanon's customs authority, the source added.
In April 2014, security forces foiled an attempt to smuggle 15 million capsules of Captagon hidden in shipping containers full of corn from Beirut's port.
Lebanon's state news agency also reported Monday's drug bust, saying the private plane was to head to Riyadh and was carrying 40 suitcases full of Captagon.
Saudi Arabia's large royal family has had past run-ins with authorities in various countries.
But authorities decided not to pursue the charge, citing a lack of evidence.
In 2013, a Saudi princess was accused in Los Angeles of enslaving a Kenyan woman as a housemaid, but the charges were also eventually dropped.
