A gift to Japan from Thailand, Hanako was born in Bangkok in 1947, but her exact birth date is unknown.
Zoo officials decided New Year's Day would be considered her birthday.
The zoo said it would hold an event celebrating Hanako's age Feb. 5, when she will be presented with home-made bread, one of her favorite foods.
Thailand presented Hanako to Japan as a "messenger of peace" in 1949, making her the first elephant to be sent to Japan after World War II, The Asahi Shimbun reported.
Hanako's daily diet consists of bananas, apples, carrots and grass, cut into small pieces since she only has one healthy tooth left.
"Hanako is still in good shape, but she's getting more wrinkles each year," zoo official Michi Amano said. "She is not good when it's cold out, so she moves into a heated pen in the afternoon."