The airline is estimated to be losing $1m a day
Aerolineas Argentinas is back in state hands 18 years after Argentina's troubled national airline was sold to the private sector.
The government approved the nationalisation of the carrier and its subsidiary Austral on Thursday.
The airline, which was owned by Spanish firm Grupo Marsans, had build up debts of $900m (£505m).
It is the latest big firm to be brought back under state ownership after a wave of privatisations in the 1990s.
The nationalisation of Argentina's flag-carrier ends a long-running saga in the country.
The deal, announced in July with great fanfare by President Cristina Fernandez de Kirchner, was welcomed by Argentines fed up with delays and cancellations.
Aerolineas is overstaffed, heavily unionised and more than half its ageing fleet of 67 planes are grounded.
But critics said the government has failed to resolve serious financial and labour woes before taking over the company.