The injection molding is one of the major process methods for fabricating specially for composite materials. This method is useful for fabricating complex shape and advanced properties of materials such as bone model, recycled plastics or building materials. A bone biomodeling requires a realistic mechanical properties and the geometry as use of mechanical tests of medical devices such as bone screw or drill. The development of bone biomodel also requires the composite materials and the method of an injection molding to produce a unified model for the tests. The mechanical properties of bone biomodeling, specially the strength or the fracture toughness have a strong relation not only to the compound condition, but also to the filling process under injection molding, because the geometry of bone has a large volume and the flow in the injection is not stable. Therefore, visualization of flow of materials in the molding is important to grasp the filling process and microstructure of the model. However, the observation of flow during the molding is hard because the molding system is, in general, not to be transparent. Ozawa et al. carried out the observation of flow behavior with tungsten fiber using micro-CT. The orientation and distribution of fibers shows the flow direction. However, the image of micro- CT scanning shows only “a result of the filling process of materials in injection”. To reveal the filling process, we develop a visible system of injection by using Poly (vinyl alcohol) (PVA) solution with good transparency and capability of changing its viscosity. Then, PVA solution can be detected by using a camera for analyzing visualization process such as particle image velocimetry (PIV). We found PVA solution is useful for investigation of relationship between flow behavior and viscosity of the material in the injection molding.