The eight-year-old daughter of Japanese heir Prince Naruhito and his wife Princess Masako has not attended Tokyo's prestigious Gakushuin school since March 1, suffering from stomach aches and anxiety attacks.
The symptoms were thought to have been induced by the actions of a group of boys in her class.
According to Japan's Kyodo news agency, the Princess and several of her classmates had been "treated harshly" by the boys, causing the Imperial Palace to intervene.
However, a representative of the school denied the Princess had been affected directly.
Accompanied by mum Princess Masako, little Aiko attended the fourth period of her morning classes, before leaving again.
Masako herself suffers from a form of depression reportedly brought on by the stress of royal life and has remained largely out of the public eye for the past few years.
The condition is thought to have been partly caused by the pressure on her to produce a male heir. Under current Japanese law only a male can succeed to the throne.