Romania has lost its second prime minister in seven months after Mihai Tudose’s own political party withdrew its backing.
The Social Democrat prime minister said he was resigning “with his head high”, AFP news agency says.
The party has been riven by a power struggle which also claimed his predecessor, Sorin Grindeanu, in June.
It has struggled to win public confidence after ballot-rigging and other corruption scandals.
Reports say Mr Tudose fell out with a powerful party colleague who, only last June, had put him forward for the post.
Recent months have seen street protests against controversial reforms of the justice system, and there have also been conflicts between politicians and anti-corruption prosecutors.
Last year, the EU’s executive warned that the country’s fight against corruption was under serious threat from political and media attack.
At the same time, Romania, one of the EU’s poorest member-states, is enjoying strong economic growth.
Romania’s 2018 budget plan envisions economic growth of 5.5% and a deficit just below the EU’s ceiling of 3% of gross domestic product, Reuters news agency reports.