The boy was attacked on Wednesday night around 8:30 p.m. PT while his family was camping near Sproat Lake about 15 kilometres northwest of Port Alberni.
His parents were cooking when they heard their son cry out. On seeing the cougar holding his son in its mouth, the boy's father hit the animal and it dropped the boy.
The boy was rushed to hospital, where he underwent surgery for a gash to the head. His injuries are said to be non-life threatening and he is expected to make a full recovery.
Insp.Chris Doyle of the Conservation Officer Service said that at 5.45 a.m. PT his officers used hounds to track and kill the cougar suspected of the attack.
"The conservation officers are confident that this was the offending cougar. It was within the immediate area of the attack site and no other scent trails were detected," he said.
Doyle is now trying to determine why the cougar attacked the boy.
"There are several factors that could have led to the attack. There may be a food shortage or the cat may have been presented with a situation that deemed that person prey for the cougar."
Doyle hopes a necropsy will provide more evidence of the attack and whether the cougar was starving.
There have been no recent reports of cougars around Sproat Lake, but an 18-month old boy was badly bitten in an attack near Ucluelet, 100 kilometres west, last August.