A rough-in assembly for mounting a free-standing faucet on a floor is revealed. The rough-in assembly includes a mounting base, a connection tube set having cold-water and hot-water connection tubes, a fixing plate, and a plurality of nuts. The mounting base consists of a bottom plate fixed on a laminated wood, a tube-fixing portion positioned on the bottom plate and provided with two locking slots, and a plurality of bolts projecting from the bottom plate and inserted through a mounting hole on the floor. The cold-water and hot-water connection tubes are locked in the two locking slots of the tube-fixing portion. The fixing plate allows the bolts of the mounting base to pass therethrough. The nuts are threaded on the bolts for fastening the fixing plate on the floor. Thereby the free-standing faucet is secured on the floor firmly and production cost is dramatically reduced.