Princess Yuriko was hospitalized after she was diagnosed as possibly suffering cerebral infarction and having aspiration pneumonia on Sunday, the Imperial Household Agency said.
The 100-year-old princess, staying at St. Luke's International Hospital in Tokyo's Chuo Ward, is in stable condition and is able to talk.
According to the agency, Princess Yuriko, aunt of Emperor Emeritus Akihito, was not feeling well due to mild dehydration on Saturday afternoon and visited the hospital on Sunday afternoon. She had some difficulty moving her right hand and leg and had a lot of phlegm. She was put on an intravenous drip in the intensive care unit on Sunday.
It has not been decided how long the princess will remain hospitalized.
She is the oldest living member of the Japanese Imperial family.