Most of students do not acquire the skill of writing especially grammar and mechanics. The writer performs a study to identify their errors for correction and improvement of their writing skills. The purpose is to find out the types of student’s errors, to discover most typical errors English writing hortatory exposition text. The scopes are only in grammar and mechanics. The writer choose Azar and Darus’ types of errors, due to their complete explanation on the details of error. In this research the writer used descriptive qualitative method. Percentage of the students’ error in writing are 22,03% = word choice, 16,38% = omit a word, 13,56% = spelling, 9,61 % = verb tense, 7,91% = add a word, 7,91% = punctuation, 7,91% = capitalization , 4,52 % = word order, 4,52% = subject/verb agreement, 2,26 % =singular-plural, 2,26% = article, 1,13% = incomplete sentence and 0,00% = word form, meaning not clear, and preposition. It is suggested this kind of error should have more attention for learning improvement by the teacher. After analyzing the student’s worksheet, it can be concluded that most students did error, mainly in word choice and omit a word.