The 86-year-old king, who has suffered from a series of ailments in recent years, is treated as a near deity in Thailand and his health is a subject of public concern.
Late on Friday he was driven from his coastal palace in Hua Hin to Bangkok's Siriraj hospital with a fever, undergoing an operation to remove his gall bladder two days later after tests revealed the organ was swollen.
Doctors reported Wednesday that the king's condition was "getting better", the Royal Household Bureau said in a statement.
Bhumibol, who is officially King Rama IX, left the Siriraj last month after a stay of almost six weeks for a check-up.
He lived in the same hospital for nearly four years after being admitted with respiratory problems in 2009 -- but there was no explanation from the palace over his prolonged stay.
Born on December 5, 1927 in the United States, Bhumibol came to the throne aged 18 in 1946 -- crowned four years later after finishing his studies in Switzerland.
