A desk includes a base and a work surface assembly mounted on the base. The work surface assembly has a board and a leg having opposite ends connected to the board and the base. The leg has an inclined section and a straight section, and the board has a first end and a second end opposite to the first end. A distance between the first end of the board and the straight section of the leg is greater than that of between the second end of the board and the straight section of the leg. The boards of the work surface assemblies are arranged in a row or two rows of a matrix. Therefore, the work surface assemblies are combinative to be mounted on the base to have various layouts of the boards.