The offer, in the region of £250,000, was made on Thursday evening and falls well short of the Fir Park club's valuation of the 25-year-old.
Moult has top scored for Motherwell with 18 goals in both seasons since his move from Wrexham.
Aberdeen have signed Nicky Maynard and remain hopeful of a deal for Shaun Maloney, while their pursuit of Stevie May appears to have stalled.
Maynard adds to manager Derek McInnes's attacking options, with forwards Ryan Christie, Greg Stewart, Adam Rooney, Jayden Stockley, Scott Wight and Miles Storey already at Pittodrie.
Moult has a year of his Motherwell contract to run and has been made an offer to extend his terms, which would make him the club's highest-paid player.
Motherwell have rejected a bid from Aberdeen to sign striker Louis Moult.