The first official state visit by an Iranian president to Lebanon has been a triumphal parade for Mahmoud Ahmadinejad.
Thousands lined the route from the airport to the Hezbollah stronghold of southern Beirut.
He pledged Iran would support Lebanon against Israel at a Hezbollah-organised rally.
Ahmadinejad also signed a 400-million-euro loan deal to fund water and power projects.
On Thursday, he will visit villages on the southern border, many of which have been rebuilt with Iranian money after the 2006 war with Israel.