Discussions are expected to focus on the sectarian bloodshed in Iraq, the crisis in Lebanon and Tehran's nuclear row with the West.
Ahmadinejad, speaking to reporters before departing from Tehran airport, said Iran is "interested in expanding" its ties with Saudi Arabia.
He said he will discuss with King Abdullah the two countries' cooperation "in the Islamic world and the region."
It is unclear how long Ahmadinejad will stay in the kingdom.
Iranian Shi'a protesting the Golden Mosque Bombing in Iraq on February 24
WHAT IS GOING ON? On March 8, RFE/RL's Washington office hosted a roundtable discussion on relations between Iraq and Iran. Although most analysts agree that Iran has been actively involved in Iraq since the U.S.-led military operation to oust former Iraqi President Saddam Hussein, they continue to debate the nature, extent, and intent of that involvement.
The RFE/RL briefing featured WAYNE WHITE, former deputy director of the U.S. State Department Bureau of Intelligence and Research's Office of Analysis for the Near East and South Asia, and A. WILLIAM SAMII, RFE/RL's regional analyst for Iran and editor of the "RFE/RL Iran Report."
LISTENListen to the complete RFE/RL briefing (about 75 minutes):
Real Audio Windows Media