This study explored the word frequency effects of plural and singular nouns in second language (L2) word processing. Although previous studies have pointed out the influence of word frequency in accessing L2 words and their corresponding concepts or the first language (L1) translations (e.g., Habuchi, 2005), they have not taken up the frequency dominance in singular and plural forms as done by Baayen, Dijkstra, and Schreuder (1997). Thus, the present study conducted two types of matching task to investigate the associations linking the L2 word, L1 translation, and the concepts of singular-dominant words (e.g., cat, photo; k = 12) and plural-dominant words (e.g., sock, bean; k = 12) on the basis of the revised hierarchical model (RHM) (Kroll & Stewart, 1994). Thirty-two Japanese learners of English participated in the study. In the experiment, the target L2 words were presented, either in singular or plural forms, on a computer screen followed by either their L1 translation (L1 matching) or a representative picture (picture-matching), and the participants were asked to judge whether the L2 word matched the L1 translation or picture. Reaction times for each trial were recorded and analyzed. The results revealed a significant interaction between the frequency dominance and word form, indicating that singular-dominant words and plural-dominant words were processed differently.