Glass beads carrying different amounts of polystyrene (PS) grafted to their surface were prepared by solution and melt-mixing processes. These beads are mixed with a nearly mono-disperse PS. The morphology of polymers filled with different volume amounts, Phi, of modified and unmodified glass beads was investigated by scanning electron microscopy (SEM). In the case of PS-grafted glass beads, the fracture surfaces show cohesive failure. The theological properties of these filled polymers were investigated by mechanical spectroscopy. The material functions, the storage modulus G’ and the loss modulus G", for PS melts filled with unmodified beads can be presented in an invariant form, i.e., independent of temperature and concentration. The temperature-shift factors follow WLF behavior, and the concentration shift factors a generalized Maron Pierce equation. The rheological material functions of melts filled with modified glass beads can be superposed for different temperatures. However, a concentration invariant representation is only possible in the frequency range belonging to the plateau region. For small frequencies, a systematic deviation occurs whose strength depends on the amount of polymer grafted to the filler surface. It is argued that this behavior may be attributed to an additional relaxation process originating from the hindered flow of the modified glass beads. This process has to be investigated in more detail in the future.