In this study, we investigated the structure and mobility of excess imidazole (Im) in a proton-conducting poly(vinylphosphonic acid) (PVPA)-Im composite material (PVPA/xIm (x >= 2), where x is the molar ratio of Im to the repeating polymer unit). The excess Im formed aggregates in PVPA/xIm that melted at similar to 60 degrees C. The mobility of Im in the aggregates and after they melted was investigated using solid-state H-1 and (CNMR)-C-13 spectroscopies. The contribution of Im to the proton conduction of the material was discussed.