Opposition leader jailed a year ago on treason charges, put under house arrest
"He was released on bail and he is under monitoring by the court," government spokesman Phay Siphan told Reuters.
Kem Sokha's daughter, Kem Monovithya, said her 65-year-old father has been placed under house arrest and was in poor health and needed medical attention.
"He has high blood sugar and he needs a long overdue surgery on his left shoulder," she said.
Kem Sokha, leader of the now-dissolved Cambodia National Rescue Party (CNRP), was arrested and accused of treason last September as part of a government-led crackdown against critics, including the CNRP.
He had been in pre-trial detention since then, held at a remote prison near Cambodia's border with Vietnam.
Former CNRP president Eng Chhai Eang wrote on his Facebook page that Kem Sokha was released from prison and "has arrived at his home". CNRP deputy president Mu Sochua said Kem Sokha had arrived home "a few hours ago".
"We don't know much more," she told Reuters.
Hun Sen's CPP won all 125 parliamentary seats in the July vote, which the United Nations and some Western countries have said was flawed because of the lack of a credible opposition, among other factors.
Fourteen government critics were freed from jail last month in a move some saw as meant to appease foreign criticism of the election.