The acquisition of noun phrase (NP) structures is considered to underpin overall second language development. Researchers have investigated the developmental process of the ability to comprehend NP structures, with a particular focus on Japanese beginner-level English as a Foreign Language (EFL) learners. In order to provide a more comprehensive picture of the developmental process, the current study collected data from Japanese learners of English with different proficiency levels ranging from beginner, intermediate, to advanced. A total of 82 Japanese learners of English were asked to complete a test created to measure their ability to comprehend eight types of NP structures in the sentential subject position. The results indicate that (a) the acquisition rates of the target NPs increase with a rise in proficiency levels, and that (b) the target NPs are completely acquired by high-intermediate and advanced level participants. These findings suggest that the acquisition of NPs can be an index of overall second language development. Some pedagogical implications toward Japanese EFL classrooms are discussed.