To provide a mounting structure of a mooring metal rack of a floating body for ensuring the safety of undersea operation required for mounting operation of the mooring metal rack mooring the floating body and for easily performing the undersea operation by eliminating the intricacy of the operation and the increase in the operation time.

A template 10 is fixed to the position at which the mooring metal rack 15 of a floating pier 2 is mounted, and a wedge-type key plate provided by a pair of key plates 11a, 11b is provided on a surface of the template 10. The mooring metal rack 15 includes a rack base plate 16 with an end portion having a shape to be engaged with the pair of key plates 11a, 11b. These key plates 11a, 11b form a dovetail groove, and an end portion of the rack base plate 16 forms a dovetail projection engaged with the dovetail groove. The floating pier 2 is positioned at a mooring site and the mooring metal rack 15 is suspended from the upper side. The mooring metal rack 15 is attached to the floating pier 2 by engaging the rack base plate 16 with the wedge-type key plate.