Italy only tabled its bid for the tournament at the start of the month.
The announcement leaves France, South Africa and Ireland as the three countries bidding to host the tournament.
The Italian Rugby Federation (FIR) said the two bids had been closely linked and it was not possible to carry on.
"As it has always been closely connected to that of the Olympic Games of Rome 2024, the candidacy for the 10th edition of the Rugby World Cup has no more conditions to continue," FIR president Alfredo Gavazzi said.
