They will host Barnsley on Saturday 21th July (3pm) with the game limited to a 6,000 capacity.
The Millers then take on Doncaster Rovers the following Tuesday 24th, 7.45pm, when the ground will be open to a maximum 9,000 supporters.
A third full capacity encounter is to be confirmed at a later date.
Stadium manager Paul Davis told the clubs official website: "We have to satisfy the local authority and emergency services that we are able to run a safe and secure matchday operation. Playing the two friendlies against Barnsley and Doncaster Rovers will give us the chance to look at all of these matters at reduced capacities of 50% and 75% respectively.
"We hope both fixtures will attract good sized crowds allowing us to carry out all of our tests robustly."
The club have also confirmed a trip to Mansfield on Saturday 4th August.