Language is a system of sounds, words, etc. used by humans to communicate thought and feelings. English has become an important language nowadays. Realizing how important language is, the Indonesian government has determined English as the first foreign language to be taught in Indonesia. As an inseparable part of speaking material, TagQuestion must be mastered by students. Sentences using Tag-Question should have a main clause, auxiliary verb, pronouns and separated from the main clause by a comma.Auxiliary verbs are often needed to help the main verb. The auxiliary verb usually stands together with the main verb, comprise the verb phrase. The Tag-Question consists of operator plus pronoun, with or without negative particle. The choice and tense of the operator are determined by the verb phrase in the superordinate clause.The researcher analyses the data statistically using statistical analysis. There is a significant correlation of the ability of students in mastering auxiliary verb to forming Tag-Question.