Monaco earned €289 million ($344 million) in profit during the summer transfer window, which led clubs in Europe's top-5 leagues.
Kylian Mbappe was sold to Paris Saint-Germain for €180 million.
Monaco earned €394 million in transfer fees while spending €105 million on replacements.
Borussia Dortmund finished second with a profit of €110 million.
Lyon at €72 million, Real Madrid at €47 million, along with Fiorentina and Sampdoria at €42 million apiece also did well.
Paris Saint-Germain paid the most with a net spend of €343 million