This study investigated the process of acquisition of syntax in Japanese as a second language (JSL) in five university students over a period of 3 years. The report begins with an overview of Japanese syntax and an explanatory model of second language learning based on human information processing. Four phases of JSL learning with 16 sub-stages are described; development of sentence and noun phrase structure in JSL is also chronicled. Results indicate that development of Japanese syntax in JSL learners is highly regular. All learners first establish basic sentence structures with copula and verb and basic categories of noun and verb. Syntactic extensions with the function of modification, then establishment of new categories, and variability of annotation of lexical items and syntactic units follow. Complexity of syntactic operations increases incrementally. Processing rules postulated in previous research were not found applicable to noun phrases and their development, which is instead dictated by characteristics inherent in the Japanese noun phrase system. Comparison of noun phrase and sentence development and the temporal relation of acquisitions shows that developmental changes on both levels are qualitatively similar, and that acquisition at the noun phrase level always precedes acquisition at the sentence level. Contains 12 references. (MSE)