Tens of thousands of flag-waving supporters recited the oath with Raul Castro at the Revolution Plaza of Santiago de Cuba, the cradle of Fidel's guerrilla struggle.
"He demonstrated that yes we could, yes we can, yes we will overcome any obstacle, threat, turbulence in our firm resolve to build socialism in Cuba,"he said.
"In front of Fidel's remains ... We swear to defend the fatherland and socialism," said Castro, who took over when his brother fell ill in 2006.
Capping a nine-day mourning period, Castro's ashes will be interred today during a "simple" ceremony at Santa Ifigenia Cemetery, near the mausoleum of 19th-century independence hero Jose Marti, his brother said.
Also Read
But Castro said that before dying at the age of 90 on November 25, his brother requested that no monuments or statues be erected in his honor, and that no streets or buildings be named after him.
"The leader of the revolution rejected any manifestation of a cult of personality," Raul Castro said.
While he was an omnipresent figure in the lives of Cubans after taking power in 1959, Fidel Castro always opposed the construction of statues of his likeness and no streets or buildings are named after him in the country.
Castro's death has fueled speculation over the direction the country may take without the man who ruled for almost half a century and left behind a divisive legacy.
After Fidel is laid to rest, all eyes will turn to Raul Castro's next move.
While he pledged to defend the socialist revolution, the president has implemented modest economic reforms, vowed to step down in 2018 and restored diplomatic ties with the United States.
Disclaimer: No Business Standard Journalist was involved in creation of this content