Surrogate births are extremely rare in Japan and banned by industry groups, but they are not illegal. The Suwa Maternity Clinic in Nagano, northwest of Tokyo, refused to provide information such as the date of the birth or gender of the baby. News reports said the baby was born last year.
The clinic said it performed the procedure because the woman's daughter has no uterus, but didn't give details on why she had that condition. The surrogate mother used a fertilized egg donated by her daughter.
"Both surrogate mother and baby were fine," said Chihiro Netsu, a spokeswoman for the clinic.
Dr. Yahiro Netsu, who runs the clinic, has long defied national opposition to such procedures, arguing that they should be an option for woman who are infertile.
In 2001, he performed what is thought to be the country's first successful surrogate birth. In 1998, Netsu was expelled from Japan's gynecology association for performing in-vitro fertilizations with eggs and sperm of donors who were not married to each other, though he was later reinstated.
The spokeswoman said the 61-year-old woman was believed to be the oldest surrogate mother in Japan, and news reports said she was the oldest woman to have given birth overall.
The Japanese Health Ministry does not release precise statistics on mothers' ages, saying only that there were two births to women aged 55 or older in 2006, the latest year that figures were available for.
Mainichi newspaper reported that the previous oldest mothers in Japan were two 60-year-old women implanted with their own fertilized eggs in the United States.
Japan Society of Obstetrics and Gynecology, a powerful body with over 15,000 members, has banned such procedures, but they are not illegal and individual clinics are free to perform them - though few actually do.
At Suwa Maternity Clinic, eight surrogate mothers have given birth. Of them, four women have delivered babies using fertilized eggs from their daughters.
The clinic will report the latest case at a conference of the Japan Society of Fertilization and Implantation later this month. It was the first time the fertilization conference had taken up the subject of surrogate births, Netsu said.