This study aims to analyze the text complexity of elementary school Korean textbooks of grades 1-6 by employing Auto-Kohesion, a Korean analysis tool, based on many linguistic and psycholinguistic measures. The results showed that text complexity gradually increased across grades by the surface-level measures (e.g., the number of sentences); however, it was not reflected by most of the other measures (i.e., cohesion measures, lexical diversity, connectives, pronouns, word frequency, modifiers). The results have pedagogical implications for the development of Korean textbooks, which aims to maximize the learning gains of Korean language learners.