The structure of bound rubber in the composites from fumed silica (A200, Nippon Aerosil Co., Japan) and polyethylacrylate rubber (PEA) was studied as a function of mixing temperature. The fraction of bound rubber in the composites increased gradually with increasing the mixing temperature from 80 to 120 degrees C, followed by saturation above 120 degrees C. High-resolution solid-state NMR results revealed that there was no chemical bonding between silanol groups and PEA molecules. Scanning electron microscope and optical microscope observation of the composites indicated that, with increasing mixing temperature, the size of agglomerates formed by silica particles decreased. Further, the molecular weight retention of PEA dropped abruptly above 120 degrees C. Dynamic viscoelastic measurements of the composites suggest that the development of network structure in the composites was greatly affected by the mixing temperature. Based on these data, structure development in composites is discussed.