Sato averaged 180.375 mph around the Iowa Speedway track. His first IndyCar pole came in his 26th career start.
Danica Patrick won the outside pole, which will be her best starting position of the season. Sato and Patrick were the only drivers to average more than 180 mph.
Tony Kanaan qualified third, followed by rookie J.R. Hildebrand and Will Power.
Dario Franchitti, who won last week's race in Milwaukee to move into a tie with Power for the points lead, will start sixth.
The race will be run Saturday.