The aim of this study was to investigate longitudinally how a child learner acquired verbal morpho-syntax in Japanese in a naturalistic second language (L2) context. Specifically the points of emergence for three verbal morpho-syntactic structures, namely verbal inflection, the V-te V structure and the passive/causative structure, were investigated within a framework of Processability Theory (PT) (Pienemann, 1998b). The subsequent development of these structures was also examined. Unlike earlier research about morpheme orders and developmental sequences in language acquisition which was criticised because of its apparent lack of theoretical underpinnings, Pienemann's Processability Theory (PT)(1998b) connects the processability of morpho-syntactic structure to linguistic theories. Pienemann also claims that this theory can be used to explain the acquisition of a wide range of morpho-syntactic structures and that it is typologically plausible and applicable to any language. In recent times PT has been extensively tested in a range of languages acquired as an L2, including German, English and Swedish (Pienemann, 1998b; Pienemann & Hakansson, 1999) and Italian and Japanese (Di Biase & Kawaguchi, 2002). The findings from these studies support this theory.