More than 1000 people from the United States and France, the country that gifted the statue in the 19th century, feted the occasion on Liberty Island in New York Harbor, complete with a statue-shaped green cake.
"She remains an inspiration for people all around the world," New York mayor Michael Bloomberg said.
"Lady Liberty is an enduring symbol of freedom, tolerance and openness that represents our country's highest ideals," Interior Secretary Ken Salazar said.
The event echoed the original October 28, 1886 inauguration of the monument in front of then-president Grover Cleveland.
The Statue of Liberty, created by French sculptor Frederic Auguste Bartholdi, was presented to the United States as a sign of friendship from the people of France.
It came to symbolise freedom - especially for immigrants, 12 million of whom passed through nearby Ellis Island as they entered the United States.
Friday's ceremony also involved 125 modern day immigrants from more than 40 countries becoming citizens, including Eloise Zinger, 30, from France.
"I feel French, but now also American," she said. "It's a very moving occasion. I came here from Paris as a student and at once I adored it."
After the American and French national anthems were played, actress Sigourney Weaver read The New Colossus, a poem by Emma Lazarus inscribed under the statue in bronze, with the famous line about welcoming "your tired, your poor, your huddled masses
yearning to breathe free".
A salute from passing boats, then a fireworks display, were to follow.
When the party is over, the landmark statue will close for a year, although Liberty Island itself will remain open to tourists, who arrive by a short ferry trip.
The $US27.25 million ($A25.5 million) renovation will improve the spiral stairway up into the crown and add safety devices and other modern requirements.
