The present study proposes an explicit instruction to teach English lexical categories to Japanese students. College-level Japanese students were tested on their knowledge of lexical categories, i.e., whether they were able to distinguish and identify four major categories: nouns, verbs, adjectives, and adverbs. Then the explicit instruction was given to them, focusing on morphological properties, i.e., types of affixes, and syntactic properties such as categories’ sentence positions, showing the effect of the instruction.