The Millers seem to be ahead of Sunderland and Peterborough in the race to sign the 26 year old centre-forward.
Ladapo signed for Plymouth last summer and scored 19 goals for them last season but those goals couldnt stop them from being relegated to League 2.
Portsmouth were showing an interest in the player last week but have been put off by his wages. The Millers are hoping to announce the deal in the next few days..