Although Japanese is rich in onomatopoeias and some of them do not  appear in the lexicon, most of them follow several patterns such as 'ABAB,' 'A B ,' and 'AB ,' 1 and they thus can be resolved by considering typical patterns.
in this paper, we introduce derivation rules and onomatopoeia patterns to the unknown word processing in Japanese morphological analysis, and aim to resolve 1) unknown words derived from words in a pre-defined lexicon and 2) unknown onomatopoeias.