In traditional linguistics, it has been assumed that the sounds of words are not related to their semantic contents, and that meanings of words are not directly linked to sensory systems. Nevertheless, many languages have a word class in which the sound and meaning of words are systematically related. In this study, by using functional magnetic resonance imaging (fMRI), we scanned brain activity in adult Japanese-speakers while they were seeing locomotion videos together with sound symbolic mimetic words, non-sound symbolic adverbs or verbs. Mimetic words were neurally processed differently from non-sound symbolic adverbs and verbs: We identified extensive bi-hemispheric activations in the regions typically associated with nonverbal cognitive processes for mimetic words but not for non-symbolic verbs or adverbs. The results suggest that mimetic words, by their direct sound-meaning link, have dual neural status both as linguistic symbols and non-linguistic iconic symbols that are directly linked to sensory experience.