Researchers pitted young chimps against human adults in two tests of short-term memory, and overall, the chimps won.
The results challenge the belief that humans are superior to chimpanzees in all cognitive functions, said researcher Tetsuro Matsuzawa of Kyoto University.
"No one can imagine that chimpanzees - young chimpanzees at the age of five - have a better performance in a memory task than humans," he said.
Mr Matsuzawa, a pioneer in studying the mental abilities of chimps, said even he was surprised.
Results of the memory testing showed that while the chimps were no more accurate than humans, they were faster.
One test included three five-year-old chimps who'd been taught the order of Arabic numerals one through nine, and a dozen human volunteers.
They saw nine numbers displayed on a computer screen. When they touched the first number, the other eight turned into white squares. The test was to touch all these squares in the order of the numbers that used to be there.

Hundreds of children gathered at the zoo, some with birthday cards for the bear that became a tourist magnet after he was rejected by his mother and rescued from her cage by a keeper a year ago.
Thomas Doerflein bottle-fed the bear and slept next to him, strumming Elvis Presley songs on his guitar as lullabies, and accompanied his every step as he was presented to the public when he was four months old.
The cuddly white cub sent Berlin Zoo's shares soaring to an all-time high on the Frankfurt Stock Exchange as visitors queued in their thousands to watch him play in his rocky enclosure.
Stuffed toy "Knut" bears sold out several times over, the cub made it onto the cover of glossy magazine Vanity Fair and Hollywood superstar Tom Cruise and his daughter Suri came to visit him, as did Leonardo DiCaprio.
But the rush to see the bear slowed as he began to put on weight and lost his cute looks. Knut now weighs a hefty 115 kilogrammes (253 pounds) and is no longer snow white.
As school children serenaded him on Wednesday, N-TV television news channel remarked that the crowds of visitors for his birthday were now an exception, reminiscent of the old days.
But the bear continues to be a mascot for the struggle to stop the ice caps melting and save the polar bear. The government used his logo in a campaign to stop global warming.
The Berlin Zoo estimates that its takings were about 10 million euros (14.7 million dollars) higher than usual last year thanks to Knut.
The national mint this week issued 25,000 special commemorative silver coins to mark his birthday