At half time Andy Caton and Paul Ince were taken off and replaced with Fola Onibuje and Aaron Brown.
Swindon had a free kick just outside the area but Paul Evans hit the ball straight into the wall.
Christian Roberts also hit the post on 55 minutes after a poor Peterborough back pass. Onibuje just couldn't reach the ball in time to put it into the back of the net.
Overall a poor Swindon game which was their worse display of the season so far. There was another good home crowd with 7,329 packing into the County Ground. Peterborough did deserve their win, although a 0-0 or 1-1 draw would also have been a fair result. Swindon's next game is away to Notts County next Saturday.