Mr Kim's Sunshine Policy led to improved relations with North Korea
Former South Korean President Kim Dae-jung is in an intensive care unit in a Seoul hospital being treated for pneumonia, medical officials have said.
Mr Kim, 85, was put on a respirator after complications arose, but is not in a critical condition, hospital official Park Chang-il said.
He won the Nobel Peace Prize in 2000 for brokering the first summit of leaders from divided Korea.
He served as South Korean president from 1998-2003.
"He became short of breath on Wednesday night and was put on a respirator around 0300 this morning," an official at Yonsei Severance Hospital was quoted as saying by Yonhap news agency.
"His condition has improved since. He is conscious, and his pulse, breathing and body temperature are normal."
Mr Kim was taken to the hospital on Monday with a fever and cold symptoms.
He dedicated his career to promoting democracy and human rights during the decades of authoritarian rule in South Korea.
His Sunshine Policy improved ties with the North during his presidency, but successors have taken a tougher line with Pyongyang and North-South relations have since soured.