Eight Japanese children with specific language impairment (SLI), eight age-matched and eight younger children with normal language development were tested with an elicited production task which involved two different kinds of morphologically complex verbs. More specifically, the verbs of focus in this study were lexical inchoatives and lexical causatives, in contrast with syntactic passives and syntactic causatives. As the names indicate, the former two are assumed to be generated within the domain of the lexicon while the latter two are assumed to be generated outside the domain of the lexicon. The obtained data revealed that the children with SLI experienced great difficulty forming the lexicon-external complex verbs, but performed relatively well on the lexicon-internal complex verbs while the performance of the age-matched and younger children with normal language development exhibited no such clear asymmetry. These results suggest that the deficit of SLI severely affects the ability to construct morphological rules that are generated outside the domain of the lexicon whereas their lexical processes remain relatively unaffected.