The present invention relates to a breakwater, particularly, to a prefabricated breakwater which is assembled in a stepped manner, having the improvements in the construction workability and prevention of the marine pollution due to the permeability of ocean currents together with the original wave dissipation function for the protection of ships or all kinds of the establishments in the harbor. The prefabricated breakwater according to the present invention comprises a plurality of unit blocks, each of which has engaging grooves at the constant distance at the top and bottom thereof, the unit blocks being assembled to form a current passage; a dissipating blocks in a plate shape having a plurality of engaging grooves at the tap and bottom or sides thereof at the constant distance; the unit blocks and dissipating blocks being assembled in a crosswise and longitudinal directions to form an hexagonal block assembly; the dissipating blocks being assembled in a stepped manner so as to be higher in an open sea direction; and the hexagonal block assemblies being connected to form a breakwater.