The 53-year-old princess - the youngest daughter of King Bhumibol Adulyadej and Queen Sirikit - was on her way to Bangkok's Kasetsart University where she was due to give a lecture when she slipped and fractured her left thigh.
The king's youngest daughter - who is a chemistry academic - was examined by a doctor and advised to go straight to Chulalongkorn Hospital where she had surgery to reset the bone.
The royal is set to remain in hospital for further treatment and physical therapy on the injury.
A statement from the Royal Household said the operation was "satisfactory, without any complications."
Her parents King Bhumibol Adulyadej, 83, and Queen Sirikit visited the princess on Monday (20.12.10) just a few hours after her operation.
Meanwhile Princess Soamsawali is being treated for pneumonia, also at Chulalongkorn Hospital.
The princess developed symptoms on Monday and was diagnosed with inflammation of the right lung.
The princess will remain in hospital to receive further treatment for the infection and will suspend her royal duties for the time being.
