"In the meeting with King Abdullah, we will discuss those issues that should be carried out jointly in the Islamic world and also the region," Iran's IRNA news agency quoted Ahmadinejad as saying shortly before leaving Tehran.
Iranian state radio said the talks would also cover "Iran's nuclear case", adding that Manouchehr Mottaki, the foreign minister, and other senior officials were accompanying the president.
US and its allies are also curious about Iran's influence in Lebanon, the Palestinian territories and Iraq, where Saudi Arabia blames Iranian-backed Shia militias for sectarian killings.
Prominence
Analysts say that Iran wants to address these concerns ahead of an Arab League summit in Saudi Arabia in late March.
A Saudi-based Western diplomat said: "Egypt, Jordan and Saudi Arabia have taken up the role of an alliance speaking in the name of the Arab world.
"So Iran is making sure its views and positions on Arab issues are heard at summits."
Saudi and Iranian officials have met several times in recent weeks to mediate between Lebanese opposition forces led by Hezbollah, a Shia group backed by Iran and Syria.
Hezbollah demands veto power in Lebanon's government and early elections, but Siniora has refused.
The standoff has paralysed parts of Beirut and occasionally led to violence.
Regional divisions
The crisis in Lebanon and Sunni-Shia fighting in Iraq has led to fears of growing sectarian divides across the region.
Saudi Arabia, Iran and Syria have accepted Iraq's invitation to a regional conference in March on easing tensions in Iraq.
Riyadh has led a drive in recent months to counter-balance Iran's influence in Lebanon, Iraq and the Palestinian territories.
The effort has been led by veteran diplomat Prince Bandar bin Sultan, who, Western diplomats in Riyadh say, is very close to the US administration.