The group's demobilisation will mark an end to Colombia's 52-year conflict that grew out of a crushed uprising over land rights.
Rebels from the Revolutionary Armed Forces of Colombia (FARC) started to gather in demobilisation zones on Tuesday to begin a historic disarmament process that marks an end to the decades-old conflict in the Latin American country, authorities said.
Rebels are due to disband with UN supervision under a peace deal with the government after 52 years of conflict.
By Wednesday, a total of 6,300 rebels were due to reach 26 disarmament zones where they will disarm and eventually re-enter civilian life.
Meanwhile, the country's last active rebel group, National Liberation Army (ELN), was taking the final steps towards its own peace talks with the government.
The two sides will begin formal peace talks in Ecuador's capital Quito on February 7, once the insurgent group frees a kidnapped politician and the government pardons two jailed rebels.
After last year's contested peace accord with the FARC, President Juan Manuel Santos said he wants a deal with the ELN to seal a "complete peace" in Colombia.
The Colombian conflict grew out of a crushed uprising over land rights in the 1960s. It has killed more than 260,000 people and left 60,000 missing, according to authorities.