The 16-year-old victim, who hasn’t been named, was taking part in the National School Games, held in Santiago de Cuba, in the west of the country.
Footage taken by a spectator shows the tragic boy in a blue vest, sparring with another boy in red.
At first, every thing seems normal as the pair trade blows around the ring.
But suddenly the boy in blue is seen bending over before falling headfirst onto the ground.
He remains lifeless as staff try to revive him by lifting up his legs and fanning him.
The other fighter can be seen celebrating his victory, punching the air and hugging his coach, before realising that his adversary is dead.
According to reports, the competition held on on Tuesday didn’t have an ambulance or first aid team on standby.
It is believed the boy, who hasn’t been named, died from a heart attack and not as a result of a blow during the fight.
According to reports he had been taking medication to lose weight, which could have caused an adverse reaction in his body.