Jason Kennedy's goal gave Rochdale back-to-back wins and left Scunthorpe still looking for a first league victory of the season.
Ashley Grimes' angled drive for the hosts and a volley from the Iron's Jimmy Ryan were the best chances in the first half.
Kennedy broke the deadlock when Grimes' curling shot was parried into his path and he tapped home from six yards.
Bobby Grant had a header cleared off the line as Steve Eyre's side held on.
VIEWS FROM THE DRESSING ROOM
Rochdale manager Steve Eyre told BBC Radio Manchester:
"Despite our early domination we re-grouped at half-time, we said it was going to be a 1-0 game and so it proved to be.
"We only allowed them to get in front of us, not behind us and the lads looked strong and were solid.
"First and foremost you'll take a win at this level and if you ask manager, and I'm no different, 1-0 is the best scoreline".