The apparently stunned animal does not react to the kicks and punches
Animal welfare authorities in Australia are searching for a boy filmed knocking a kangaroo to the ground.
In the video, which was posted online, the boy is shown punching and kicking the apparently dazed kangaroo, as his friend laughs from behind the camera.
It is unclear whether the attack resulted in the death of the animal.
Appealing to media outlets to publicise the attack, the RSPCA said they wanted the culprits to be "caught, charged and prosecuted".
The film of the attack was sent to the RSPCA in the state of Western Australia.
In it, the boy is shown aiming kick-boxing-style kicks at the kangaroo, then pulling it towards him so he can knee it in the chest.
The final aggressive punch sends the kangaroo to the ground, unconscious or dead.
Wildlife experts said the kangaroo appeared stunned, and had possibly just been hit by a car.
They said ordinarily kangaroos would have fled in the face of such an attack.
The RSPCA said the vicious nature of the attack had prompted it to launch a nationwide search for the two boys.
"We are appealing to every media outlet in Australia to help us track down the cowards behind the vicious attack on this kangaroo," RSPCA Queensland spokesman Michael Beatty said.
"Thankfully this sickening footage has now been removed from the website where it was first seen.
"The next stage is to ensure that those responsible for this film are brought to justice.
"Only a coward would attack an injured and obviously terrified young animal much smaller than himself.
"We want these cowards to be caught, charged and prosecuted."