The R116 black box has been recovered by divers working in Blacksod.
The data recorder was found by navy divers who were examining the wreckage of the helicopter, 40 metres underwater.
The R116, which crashed on the Mayo coast last week, was searched by divers today thanks to favourable weather conditions.
The Air Accident Investigation Unit has said the recorder was recovered from the seabed just off Blackrock this afternoon.
It is currently in the custody of the AAIU and will be transferred to the UK tomorrow for further examination.
Authorities said no bodies of three missing crew have been found with the wreckage east of Blackrock island, about 13km off the coast of Co Mayo.
The Sikorsky S-92 is believed to have hit the island before crashing into the sea in the early hours of March 14.
The body of Captain Dara Fitzpatrick, a 45-year-old mother-of-one, is the only one of the four crew to have been recovered from the ocean so far.
The other crew members, Captain Mark Duffy, Winchman Ciaran Smith and Winch Operator Paul Ormsby, remain missing.
The black box recorder was taken from the seabed at 4.30pm.
Jurgen Whyte, chief inspector with Ireland's Air Accident Investigation Unit (AAIU), said the unit appeared to be in good condition.
"It was always a priority to recover the three crew members however there are protocols within our work - where we see a recorder we are obliged to take the recorder," he said.
"The concern was that if we did not take it at the time we would not get it."
"Now our focus is to continue with the operation to seek and recover the three remaining crew members."
Earlier: Dive teams have begun searching the wreckage of a Coast Guard helicopter for its three missing crew after it crashed into the Atlantic over a week ago.
Working in pairs and attached to a ship on the surface by umbilical cables for air and communications, divers have nine or 10 minutes on the seabed.
A dive platform has been set up above the crash site - about 60 metres to the east of Blackrock island, off the coast of Co Mayo.
The Sikorsky S-92 is believed to have hit the island before crashing into the sea in the early hours of March 14.
Captain Dara Fitzpatrick, a 45-year-old mother-of-one, is the only one of the four crew to have been recovered from the ocean so far.
The other crew members, Captain Mark Duffy, Winchman Ciaran Smith and Winch Operator Paul Ormsby, remain missing.
Superintendent Tony Healy said there is no indication yet if the bodies of the three missing crew are with the wreckage.
"Conditions are close to ideal. Diving has commenced and we are awaiting reports back," he said.
"It's a delicate operation. It's a dangerous operation for the divers. We're operating with their safety in mind at all times."
Visibility on the seabed is said to be good.
On the surface conditions are calm under hazy skies and little wind.
The Irish Lights Vessel Granuaile is positioned next to the dive platform and carrying a recompression chamber in case of emergencies.
A shot line has been dropped next to the wreckage for divers to traverse.
Divers are also obliged to bring the black box flight recorder to the surface if they see it.
Derek Flanagan, divisional controller based at Malin Head for the Coast Guard, said communications between the divers and from them to the surface were key for a methodical search of the wreckage.
"You are talking about a 40 metre dive and about nine minutes bottom time," he said.
"We have such a small amount of time down there that every minute is crucial so we don't waste time when we get down there and get the job done and find these people."
The first dives began at about 11.30am.
The helicopter is lying in an area from where signals from the black box flight recorder are being emitted.
The Air Accident Investigation Unit (AAIU) has said it believed the tail of Rescue 116 hit rocks on the western end of the island, about 13km (eight miles) off the Mayo coast as it returned from supporting a rescue mission to refuel at Blacksod.
There was no indication of any danger moments before the Sikorsky S-92 vanished, with the crew's final transmission: "Shortly landing at Blacksod."
