Jesus Alfredo Guzman Salazar, 29, reportedly was freed late Friday along with the five other men with whom he was kidnapped from a bar, a relative who requested anonymity for security reasons told AFP.
"They were negotiating all this time, but now are free and well," the source said, adding that some of the captured men were already back in Sinaloa state.
Guzman Salazar -- one of Guzman's sons from his first marriage -- was attending a celebration early Monday at an upscale restaurant and bar in the resort city of Puerto Vallarta when gunmen in pick-up trucks swooped in and kidnapped him and five of his six companions.
Several women who were also at the fete were allowed to leave unharmed.
The younger Guzman -- himself a key operator in the Sinaloa cartel who is wanted for arrest under a 2009 warrant -- was identified by the Jalisco state prosecutor's office based on security camera footage.
Notified by AFP about the reported release, the Mexico Attorney General's office said simply that it is "still working on the investigation."
Authorities had said they suspected the gunmen who seized the men were from the Jalisco New Generation cartel, an upstart rival of the Sinaloa cartel.
Jalisco New Generation has grown into a powerful force in recent years, spreading into Asia and Europe and defying the authorities with attacks and ambushes. Last year it brought down an army helicopter with a rocket launcher, killing seven soldiers.
The governors of western Jalisco and Sinaloa states, where the two crime syndicates are based, have warned of possible reprisals or even a full scale warfare between the drug cartels if Guzman Salazar was not released.
Violent but 'cleanly done'
There was still no word as to who is responsible for the kidnapping, but government officials said earlier this week that they were investigating the possible involvement of municipal police in the resort of Puerto Vallarta.
Security camera footage of the abduction showed armed men bursting in and making their victims kneel down with their hands on their heads before taking them away.
"It was violent but cleanly done," the restaurant's owner Ignacio Cadena Beraud told reporters earlier this week, describing the brutal precision of the abductions.
'El Chapo' Guzman was head of the powerful Sinaloa cartel and one of the world's most notorious criminals until he was recaptured and imprisoned in January.
Guzman was arrested in 2014 but staged a spectacular jailbreak one year later, becoming for a period the world's most-wanted man.
He is now being held in a maximum security federal prison in the northern city of Ciudad Juarez and fighting extradition to the United States.
The Mexican government gave the green light to extradite Guzman after US officials promised that he would not face the death penalty, a punishment outlawed in Mexico. Legal maneuvers however continue to try to avoid his extradition.
Nevertheless the United States expects Guzman to be extradited by the end of the year, a US official told AFP, which would be a relatively short period for this type of procedure.
