Biles posted a total of 14.800 in the balance beam final for her impeccable routine ahead of China's Zhou Yaqin with 14.700.
Brazilian Rebeca Andrade, who beat Biles on Saturday to gold in the women's vault, posted 14.300 for bronze.
The American claimed her second gold of the day in the floor final with 14.633, 0.133 points ahead of second-placed Andrade.
"I wasn't too worried about medal count or medal colour," Biles said.
She also won gold on balance beam and floor exercise after clinching silver on vault.
Persons:
Simone Biles, Yves Herman Acquire, Biles, China's Zhou, Rebeca Andrade, Andrade, Flavia Saraiva, I’m, JARMAN Jake Jarman, Britain's, Jarman, Young, Germany's Lukas Dauser, Japan's Daiki Hashimoto, Anita Kobylinska, Ken Ferris
Organizations:
Rights, U.S, Young, Thomson
Locations:
Antwerp, Belgium, Rights ANTWERP, China's, American, Gdansk