Olaseni scored 14 points and had 10 rebounds for the Hawkeyes (16-4, 5-2 Big Ten), who shot 51.9 percent from the field against an usually stingy Northwestern (10-11, 3-5) defense.
Roy Devyn Marble also scored 14 for Iowa and Mike Gesell added 11.
Drew Crawford scored 20 points and Tre Demps had 11 for the Wildcats, who had won their previous two games.
Iowa led 30-24 at halftime, but a 3-point shot by JerShon Cobb early in the second half cut the lead to three points. Iowa responded with an 11-3 run that opened some space. The Hawkeyes put together an 11-0 run later in the half to keep the game out of reach.