This study explores sound-symbolic, or mimetic, words in the Japanese language, the majority of which are never entered in Japanese dictionaries, and which may not be fully understood in all their nuances by native speakers. The extensiveness of the sound-symbolic system is related to the semantic under-differentiation of Japanese verbs. An introductory chapter states the problem, gives an overview of the study of sound symbolism, delineates the language corpus used, discusses linguistic varieties in Japanese, and explains terminology, transcription, and data sources used. An overview of the Japanese sound-symbolic system follows, focusing on the syntactic, prosodic, melodic, and phonological properties of mimetic forms. The third and fourth chapters look in greater detail at the sound symbolism of mimetic adverbs based on two root types. Chapter five explores some historical considerations related to the phonology of mimetic words. A final chapter discusses iconicity and linguistic structure and draws conclusions from the previous discussion. Contains 86 references. (MSE)