Blues made an approach for the 22-year-old centre-back but their bid was rejected.
Part of a statement from Rovers chairman John Ryan on the official Doncaster website reads:
"Doncaster Rovers' Board of Directors have this afternoon turned down a substantial bid for centre-back Matthew Mills from Championship rivals Birmingham City.
"The rejection of the bid reaffirms the importance of Matthew Mills to Doncaster Rovers.
"Both the management and Board feel that Matt is integral to the progress of the Club."