Misao Okawa said Wednesday that she was "very happy" to receive the recognition and a certificate from Guinness World Records.
After a meal of her favorite mackerel sushi, Okawa nodded off as she sat in her wheelchair, her 3-month-old great grandson, Hibiki Okawa, at her side. But she woke up to speak to a reporter.
Asked for her secret for longevity, she said it was to "watch out for one's health."
The recognition by Guinness World Records was a nice gift for Okawa, who will mark her 115th birthday next week. According to the Gerontology Research Institute, which verifies age information for Guinness, she was born March 5, 1898.
Okawa lives in a nursing home in Osaka. The manager there, Tomohito Okada, said Okawa eats whatever she likes.
The world's oldest living person as recognized by Guinness—115-year-old Jiroemon Kimura—also lives in Japan.
Japan has the most centenarians in the world, with more than 51,000, according to the government. More than 87 percent of them are women.
Okawa was married in 1919 to her husband Yukio and had three children—two daughters and a son. She now has four grandchildren and six great grandchildren.
Okawa's 90-year-old son, Hiroshi, said that though inherited some of his mothers' genes, he doubted he would manage to match his mother's longevity.
"On my father's side, there are some who lived long and some who don't—like my father who died at 36—so I doubt I'll live as long," he said.