The former chief minister was admitted for a "minor procedure - change of (Percutaneous endoscopic gastronomy) PEG tube," Kauvery Hospital Executive Director S Aravindan said in a statement.
After the completion of the procedure which took about 40 minutes, Mr Karunanidhi was discharged, hospital sources said.
Mr Karunanidhi's family members were present at the hospital during his brief hospitalisation.
His daughter Kanimozhi later told reporters that the tube has to be replaced once every six months and that he was fine.
Once he was treated for nutrition and hydration support and the second time, he underwent tracheostomy to optimise his breathing.
Congress vice-president Rahul Gandhi, former Union Minister P Chidambaram, AIADMK leaders M Thambidurai and D Jayakumar were among several leaders who had visited him during his hospitalisation.
The top DMK leader has been out of action ever since he took ill last year. Party affairs are being taken care by his son, DMK Working President MK Stalin.