Thousands gathered in the Argentine capital Buenos Aires to show their support for outgoing President Cristina Fernandez who lost to conservative Mauricio Macri in a run-off last month that will bring an end to 12 years of leftist rule.
Fernandez, a powerful woman leader who held power in Argentina for eight years, is revered by many Argentines for increasing welfare benefits.
During her speech outside the La Casa Rosada Presidential Palace in Buenos Aires, she thanked tens of thousands of cheering supporters and vowed that she will stay by their side.
"We believe in what we have achieved so we need to have a positive attitude to ensure that these things will not be destroyed," she said, and added "When you feel that those who you trusted and voted for have betrayed you, take up your flags."
"These are the greatest things that I have given to the Argentine people - the empowerment of the people, of the citizens, the empowerment of liberties, rights. Thank you for so much happiness, so much joy, so much love. I love you all. You will all be with me forever in my heart, and know, that I will always be right there with you. Thank you everyone."
During her speech, Fernandez joked: "I can't talk much because after midnight I'll turn into a pumpkin."
Fernadez's opponents claim she created a handout culture and congested Latin America's third largest economy with interventionist policies while her rival Macri has vowed to remove state controls on the economy and implement more orthodox policies.
Conservative Mauricio Macri who inherits problems including high inflation and a low level of foreign currency reserves is due to be sworn in as president later.
Fernandez is not to attend Thursday's swearing-in after the two became embroiled in a row over the ceremony place and it will be the first time since the end of Argentina's military dictatorship in 1983 that a president has skipped the inauguration of a successor.
Macri who has not given the details of his economic policies, but declared that radical changes are needed to build trust in the market, is the first centre-right leader to come to power since Argentina returned to democracy.
Meanwhile, Fernandez's party still keeps the most seats in the legislature, which could make it hard for Macri to practice big regulations.