A block assembly for constructing a seawall and dissipating waves. The block assembly includes a block comprising a front wall, a left side part and a right side part. The left and right side parts include stepped surfaces and a plurality of round shaped projection parts are closely disposed on the front wall. The block further includes two connecting walls having male protrusions and female recesses formed on upper and lower surfaces thereof. A vertical partition wall extends from a rear center of the front wall and includes a male protrusion on the upper surface thereof and a female recesses on the lower surface thereof