ABSTRACT Hafifatul Ichtyar Rizqina, 2020. entitled The Effect Of First Language Stimuli In English Vocabulary Mastery Of Young Learners At 5-6 Years Old at TK Al-Kautsar Pamekasan. Undergraduate, Thesis, English Teaching Learning Program (TBI), State Islamic Institute (IAIN) of Madura. Advisor: Mulyadi, S.S., M.Pd. Key Words: First language stimuli, Vocabulary mastery, Young learner’s I…