Assembly-box concrete hollow floor is a new kind of cellular voided floor structure, in which a lot of prefabricated box-shaped interior forms are placed regularly on the formwork before the floor concrete is cast. The new type of box-shaped filler is termed assembly-box and could behave as load-bearing elements. Such floor system has many advantages, such as low self-weight, good mechanical behavior, equally flexural stiffness in two directions and high voided rate. The characteristic of this floor structure is the combination of precast assembly-box and cast-in orthogonal grids of ribs. For the purpose of understanding the behavior of this floor, a test has been carried out with three scale specimens under vertical loading. All experimental values provide essentially the same result that a typical flexural failure occurred under ultimate load and the structural system of assembly-box hollow could behave like an overall cast-in hollow floor. A part of the top plate in assembly-box could be viewed as the flange of rib beam during the process of structural design.