missing in Guerrero state has been identified from charred remains, an official says.
A family member of one of the students, Alexander Mora, confirmed that the remains identified were his.
The relative said the family had received the information from a team of forensic experts.
The students were allegedly seized by local police in the town of Iguala in September and given to a criminal gang.
Prosecutors say the gang killed them and burned their bodies at a rubbish dump near the town of Cocula before scattered their ashes in a river.
The students' disappearance has triggered widespread protests across Mexico against corruption and violence.
Another demonstration was held on Saturday in Mexico City at which parents of students spoke about the identification.
"If [the government] thinks that, because one of our boys' DNA was identified, we will sit and cry, we want to tell them that they're wrong," Felipe de la Cruz, father of a missing student, told the crowd.
"We will keep fighting until we find the other 42."
The unrest has seen President Enrique Pena Nieto's popularity rating drop to its lowest point since he took office two years ago.
In response, he has submitted a package of reforms to Congress that include replacing all 1,800 municipal police forces with state-level units.