The aim of this study is to construct a model of a simple lexical network showing the strength and asymmetry of the connections between vocabulary items in the L2 mental lexicon of Japanese learners. The study focuses on eight nouns and investigates how they are networked, and whether the existing network structure formed by these nouns would be affected by the introduction of an adjective. Data in the form of perceived relatedness of the nouns collected from 17 Japanese EFL learners at different proficiency levels are analyzed using AMISESCAL (Asymmetric von Mises Scaling). AMISESCAL is a newly developed statistical model that visualizes asymmetric relations among elements on a two dimensional map. Both strength and asymmetry of the connections among vocabulary items are explicated using this model; distinctive features of the EFL learners' mental lexicon are thus obtained. The varieties of L2 network structure and the differences between individual learners are discussed.