This study aims to: (1) explain the contribution of learning motivation to the writing skills of exposition text of class X MAN 1 Bukittinggi students; (2) explain the contribution of vocabulary mastery to the writing skills of exposition text of class X MAN 1 Bukittinggi students; (3) explain the contribution of learning motivation and vocabulary mastery to the writing skills of exposition text of class X MAN 1Bukittinggi students. The sample of the study of the total population in each class is 43 students. The data of this research are the score taken from the result of learningmotivation questionnaire, the score of vocabulary test, and the score of test of exposition text writing skill. Based on the results of the research, it can be concluded that the motivation of learning and mastery of vocabulary can be used as a predictor to improve the results of learning skills of writing exposition text. Therefore, to improve learning outcomes in writing skills, the students are given the motivation to learn writing and mastering vocabulary.