Boero, 38, sustained fatal injuries in a fall during the first stage in western Argentina, organisers say.
The annual off-road race, originally from Paris to Dakar in Senegal, moved to South America in 2009, largely because of security concerns.
Most of the participants are amateur motorcyclists and car drivers, running against experienced racers.
It was the second Dakar rally Boero had taken part in.
Organisers say he was killed when he came off his bike during the stage between the Argentine cities of Mar del Plata and Santa Rosa de la Pampa on Saturday.

A Commons Justice Committee report says offenders aged between 18 and 25 are 10 times more likely to have a learning disability or autistic disorder.
It said a "lack of action" on these offenders had led many to re-offend.
The government said "significant efforts" had been made to prevent young people ending up in prison.
The committee's report argues there is a strong case for treating young adult offenders differently because their brains are still developing up to the age of 25 - meaning they are more likely to act impulsively and not weigh up the long-term effects.
It also found those still offending into adulthood were more likely to have learning difficulties or communication disorders, or to have suffered head injuries.
It said flawed interventions, set up by the Ministry of Justice and carried out by the National Offender Management Service, did not recognise young adults' needs and prevented them getting out of a cycle of crime.
The young adults tired of offending
The terror of young offender institutions
The number of young adults in the criminal justice system, who are mostly men, has fallen in recent years, but figures suggest 18 to 25-year-olds still account for up to 40% of the criminal caseload.
They also have the highest reconviction rate, with 75% returning to crime within two years of being released.
But the report argued that, while those in this age group offended the most, they also had the greatest potential to stop offending as they "grow out of crime".
It said age and maturity should be taken into significantly greater account within the criminal justice system and should presume that up to the age of 25 young adults were typically still maturing.
The committee said it welcomed the Ministry of Justice's commitment to develop a maturity assessment when dealing with young offenders but said that not screening for mental disorders and learning and communication needs was a "missed opportunity".
"This is short-sighted as such screening would enable a thorough understanding of individual needs and underpin better informed commissioning decisions for the services young adults need to address their offending," the report said.
Alex Hewson, of the Prison Reform Trust, said: "A justice system which throws young people off a cliff edge on their 18th birthday, and expects them to fend for themselves in the adult system when they are still maturing and often vulnerable, is not one that is set up to deliver for offenders, victims or local communities."
A Ministry of Justice spokeswoman said: "Significant efforts have been made to divert young people from custody and this has resulted in a welcome reduction in the prison population - down 40% since 2010. But those in custody are in for longer and for more serious offences.
"We recognise the specific challenges associated with this age group and are committed to addressing these."
Argentine motorcyclist Jorge Martinez Boero has died in an accident on the opening day of the Dakar Rally.
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There needs to be a major change in dealing with young adult offenders, MPs have said, based on evidence that shows their brains are still developing.