Obama has said he is willing to hold direct diplomacy with Iranian leaders as a way to break the impasse between the two countries or give the U.S. more credibility to press for tougher sanctions if talks fail. His policy marks a departure from the Bush administration, which has refused high-level engagements with Iran.
In his comments, Ahmadinejad congratulated the Democrat on "attracting the majority of voters in the election." The text of Ahmadinejad's statement was carried by the official IRNA news agency.
Ahmadinejad also said he hopes Obama will "use the opportunity to serve the (American) people and leave a good name for history" during his term in office.
Iran and U.S. have no formal diplomatic relations since 1979 and the hostage drama when militant Iranian students held 52 Americans captive 444 days.
Current U.S.-Iranian relations remain tense, with Washington accusing Iran of trying to develop nuclear weapons and of providing support for Shiite militants who are killing U.S. soldiers in Iraq - charges Iran denies.
In Jerusalem, Israeli Foreign Minister Tzipi Livni, a contender for prime minister in her country's elections, warned against any dialogue with Iran - a first sign of Israeli disagreement with the incoming U.S. administration.
"Dialogue at this time is liable to broadcast weakness," cautioned Livni, who is head of the governing Kadima Party. "I think early dialogue at a time when it appears to Iran that the world has given up on sanctions could be problematic."
Israeli officials describe Iran as the biggest threat to the Jewish state's existence, citing Ahmadinejad's frequent calls for Israel's destruction and its development of long-range missiles capable of striking the Jewish state.
Livni has repeatedly said she hopes international diplomacy prevails. But she doesn't rule out force if U.N. sanctions don't pressure Iran to scale back its nuclear aims. In June, she said Iran "needs to understand the military threat exists and is not being taken off the table."
Iran sees Obama's victory as a triumph over the unpopular policies of U.S. President George W. Bush, who repeatedly clashed with Iranian leaders while in office over Iran's nuclear program and its opposition to the U.S.-led invasion and occupation of Afghanistan and Iraq.
Ahmadinejad went on in his Thursday message to say that "nations of the world" expect changes from Obama - mostly that he will change current U.S. foreign policy.
That policy, Ahmadinejad claimed, was "based on warmongering, occupation, bullying, deception and humiliation, as well as discrimination and unfair relations" and has led to "hatred of all nations and majority of governments toward the U.S. leaders."
Ahmadinejad also said that Obama is expected to replace such a policy with "an approach based on justice and respect, as well as lack of intervention in the affairs of others."
Iranians will welcome such changes, Ahmadinejad added. Iran's government refused to publicly side with any of the U.S. candidates throughout the presidential race, although Parliament Speaker Ali Larijani said last month that Obama seemed "more rational" than John McCain.
Saeed Leilaz, an independent analyst in Tehran, said Ahmadinejad's message was a "positive step" that now leaves Washington with the responsibility for the next one. Leilaz added he believes Obama's victory will "weaken radicalism" in Afghanistan, Iraq, Iran and North Korea.
Associated Press Writer Amy Teibel contributed to this report from Jerusalem.