The prime minister of Kyrgyzstan has resigned just 18 days before a parliamentary election.
Mr Atambayev was leaving on "good terms" with the president
Almaz Atambayev, then an opposition leader, was drafted into the government in March to quell growing unrest.
A government spokesman said Mr Atambayev had left on good terms with President Kurmanbek Bakiyev.
The Central Asian nation adopted a new constitution last month after a referendum that observers criticised for ballot irregularities.
Critics say the changes are designed to bolster the president's influence in parliament, but he says the reforms will help clarify the separation of power.
Following the referendum, Mr Bakiyev called a snap election for 16 December.
Mr Atambayev was a moderate opposition leader who had led anti-government protests before his elevation in March.
Demonstrators had called for the president to step down, and Mr Atambayev's appointment was seen as an attempt to appease the government's opponents.
His time as prime minister was not without controversy - he claimed to have received death threats over a plan to nationalise a semiconductor plant.
And in May he said he was poisoned and fell unconscious for two days, blaming "some government official" for the incident.
Kyrgyzstan has suffered political upheaval for a number of years.
President Bakiyev replaced Askar Akayev, who was accused of corruption, in 2005.
But President Bakiyev has suffered growing unrest amid claims of cronyism and of failure to fight corruption.