Liam Lotter said he found the piece during a family vacation in the east African nation in December.
"We stumbled across what seemed like a curved sort of gray object," the 18-year-old told CNN by phone. "We didn't know what it was at first."
Investigators will examine it to establish whether it's from Malaysia Airlines Flight 370, said Dan O'Malley of the Australian Transport Safety Bureau.
The jetliner vanished on March 8, 2014, after it took off from Kuala Lumpur, Malaysia, en route to Beijing, with 239 people aboard.
It disappeared in airspace over the Gulf of Thailand, and it has not been seen since.
Australia is leading the underwater search effort
in the southern Indian Ocean for the Boeing 777 aircraft.
From South Africa to Australia
Lotter said South African aviation officials plan to pick up the piece next week from his house in Wartburg, a South African town about 60 miles (100 kilometers) northwest of Durban.
It will be transported to the Australian agency's laboratory in Canberra for analysis by investigators from Malaysia, Australia and South Africa, according to O'Malley. Boeing engineers will also join the investigators.
Lebo Madiba, a South Africa Civil Aviation Authority consultant, said she's not sure when the piece will be picked up from the teenager.
But once authorities have it in their possession, she said, it will be sent to Australia for examination.
'You can actually see the serial number'
The teen said he stumbled across the piece while walking with his cousin on December 30. The family was on vacation in Mozambique's Inhambane district, which is across a bay from Maxixe.
His cousin said the piece looked like part of an airplane. It's between 3 to 4 feet long and made from stainless steel, Lotter said.
The debris also has holes from, he presumes, bolts that once attached it to the rest of the plane.
"You can actually see the serial number and code," he said. "It's quite light."
After discovering it, Lotter and his cousin hauled the piece back to the family beach house. His relatives were skeptical, and speculated it's probably from a boat, not a plane.
When their vacation ended on January 5, they tucked it away in their boat and sailed back to South Africa.
"We stuck it in the back of the boat," Lotter said. "So we take this thing, and when we got back we stored it in a storage room where we put all our outdoor stuff."
Then school started, and he completely forgot about it.
Last week, his uncle showed him a story about an American man who found another suspected plane piece
"That's what made me think about it again," Lotter said.
His mother contacted Australian and South African officials to pick it up. A radio station also interviewed the mother and son, thrusting them into the spotlight.
Other pieces found
Meanwhile, aviation experts will examine the other plane debris found by a U.S. tourist last week, also along the Mozambique coast. That piece is from the horizontal part of an airliner's tail.
Officials have not said yet whether that plane part matches up with MH370.
But the debris could be from a Boeing 777
, according to a U.S. official. And its location off Mozambique is consistent with some of the drift modeling, Australian authorities said.
Investigators have said another piece of debris found last year on Reunion Island, which sits in the Indian Ocean, could also belong to the Malaysian jet.