The proposed study aims to investigate whether second language (L2) learners can acquire implicit knowledge of English articles, which has been found to be problematic especially for L2 learners whose first language does not possess articles. The current study employs the visual-world paradigm, which tracks eye-movement to a visual context during online sentence processing. The advantages for visual-world paradigm for measuring implicit knowledge are discussed. We focus on the two grammatical functions in the English article system: definiteness and countability. Definiteness refers to whether a referent is uniquely identifiable (definite) or not (indefinite). Countability refers to whether a referent has distinct boundaries (e.g., a count noun like “three books”) or does not have distinct boundaries (e.g., a mass noun like “some spinach”). In this talk, I report the results from the pilot study on English native speakers. Then, I propose the main research design for L2 learners to explore explicit and implicit learning processes by comparing explicit/implicit knowledge and explicit/implicit learning aptitudes.