Their cases bring to 97 the number of executions of locals and foreigners carried out in the conservative Muslim kingdom this year.
That compares with 87 for all of 2014, according to AFP tallies.
The Syrian, Mohammed Hussein Abdulkareem Halwani, was executed in Jubail, on the kingdom's Gulf coast, after a court found him guilty of smuggling methamphetamines, the interior ministry said.
The ministry, in statements carried by the official Saudi Press Agency, named the two Saudis executed as Hussein al-Qahtani and Jibran al-Qahtani.
Also Read
Under the Gulf state's strict Islamic sharia legal code, drug trafficking, rape, murder, armed robbery and apostasy are all punishable by death.
But Christof Heyns, a UN special rapporteur whose mandate includes extrajudicial, summary or arbitrary executions, told AFP last month that "it seems that many of these trials are in secrecy and that lawyers are not available and they do not comply with the standards of fair trial."
The Saudi interior ministry has cited deterrence as the reason for carrying out the punishment.