The IOC said Pulaku tested positive for a banned steroid, stanozolol, on July 23, and that a backup "B'' sample confirmed the result.
The announcement came a day after Albania dropped the 19-year-old from its weightlifting team over doping suspicions. He was supposed to have competed in the 77-kilogram category.
IOC spokesman Mark Adams said Pulaku was tested in London, and has had his accreditation taken away and been kicked out of the athletes village.
"It's always a sad day when a cheating athlete is caught. We hope there will be no more but the message is very clear: if you're doping we're going to catch you. There will be 5,000 tests during these games. All the medallists will be tested."
In a hearing Thursday the lifter's coach and uncle, Sami Pulaku, "explained that neither he nor the athlete understood how such substance ended up in the body of the athlete," the IOC said.
Two Turkish lifters were also dropped by their federation at the last minute after failing doping tests.
The weightlifting competition begins Saturday with the women's 48-kilogram category.
Weightlifting has a troubled history when it comes to doping. Despite attempts to clean up the sport, several top competitors have tested positive in recent years, including former Olympic and world champion Nurcan Taylan of Turkey and Liao Hui, the 2008 Olympic champion in the men's 69-kilogram class. Both are serving doping bans and will miss the London Games.
So far, Adams said, the IOC has taken 1,001 total samples in London — 715 urine and 286 blood.
"We do target the key sports where we have suspicions and key athletes where we have suspicions," he said.
The World Anti-Doping Agency said earlier this week that 107 athletes had been busted for doping in the six months leading up to the Olympics and kept out of the games.
AP Sports Writer Stephen Wilson contributed to this report.