This research project implemented an exploratory factor analysis (EFA) of the construct validity of a grammaticality judgment test (GJT) as a tool to measure Korean language learners' grammatical knowledge. Focusing on passive expressions in Korean, we developed two distinctive tools for implicit and explicit knowledge, along with three types of GJTs with different variables of time, modality, and stimuli. The EFA with two latent variables was implemented to examine how the test types would be grouped according to components. The results revealed that ungrammatical and grammatical sentences in each test converge to different factors, suggesting that the measurement of the learner's knowledge type may depend on grammaticality of stimuli. The results highlight the importance of carefully controlling the grammaticality of sentences as a factor in designing GJTs.