About 30,000 people were killed during Peru's era of terror
"The testimonies will be a vehicle to enable Peruvians to understand, to feel, what those people caught in the middle of the political and subversive violence lived through," commission member, Sofia Macher, was quoted by the Associated Press news agency as saying.
Between the mid-1980s and early 1990s, Peru was racked by violence between Marxist guerrillas and government troops desperate to enforce the order.
The commission - which has no legal powers - will hear cases involving hundreds of deaths, including the killing of at least seven journalists in 1983.
Atrocities
The rebels from the Shining Path movement and also the smaller Marxist group - the Tupac Amaru Revolutionary Movement - waged parallel wars to impose communism during the two decades of violence that spanned three elected governments.
Shining Path rebels terrorised villages by massacring peasants who refused to join their fight.
The Peruvian army responded by launching an onslaught against the rebels, and is accused of many atrocities.
The army is also suspected of often burying the guerrillas in mass graves to cover their tracks.
The violence wound down in 1992 after the government captured the founder of Shining Path, Abimael Guzman.
Dirty war
Some of the crimes the commission will be examining are horrific, with victims recounting how they were forced to watch savage executions of their relatives.
One of the blackest periods of violence that the commission will examine is the 1996 prison riots, in which 400 Shining Path rebels were killed by the military.
"If the wars are considered dirty, then this war is especially dirty and terrible," head of the commission, Salomon Lerner, told the Reuters news agency.
"What is absolute, what is definitive is that people were unjustly killed and human rights were violated. We are not trying to open Pandora's box, we are trying to air things that have been forgotten and stink," Mr Lerner said.
The commission - which was set up last year and is expected to end its inquiry next year - has also a mandate to identify the missing people and compensate the victims.
Representatives from the United Nations and the Organisation of American States were expected to attend the hearings.