A cooling structure in a cylinder head of a water-cooled multicylinder engine has partitions disposed between cylinders and in a water jacket defined in the cylinder head, cooling inlet ports disposed on one side of plug insertion tubes extending vertically and disposed above substantially central portions of the cylinders and a cooling water discharge port disposed on the other side of the plug insertion tubes, and walls projecting from the partitions toward the plug insertion tubes. Each of the walls includes a lower projecting portion having a relatively small width near a wall of the cylinder head above a combustion chamber defined in each of the cylinders and an upper projecting portion having a relatively large width.