Abstract Name : Fie Asfarina Student’s Number : 0906102050035 Study Program : English Title : Teaching Writing Skill by Implementing Authentic Assessment through Self Assessment (An Experimental Study at SMAN 1 Montasik, Aceh Besar) Keywords: Authentic Assessment, Self Assessment, Writing Skill This thesis entitles “Teaching Writing Skill by Implementing Authentic Assessment through Self Assessment.” One class pre-test and post-test experimental design was applied in conducting this study at SMA Negeri 1 Montasik, Aceh Besar. This study is intended to find out whether implementing the authentic assessment through selfassessment can improve students’ writing skill in the hortatory text. The population of the study was the second year students of SMA Negeri 1 Montasik, Aceh Besar, and the sample of this study was the students of class XI IA-1 that consisted of 20 students and only 18 students as the sample in the experiment. The instrument used to collect the data was tests (pre test and post test). From these tests, the researcher found that the mean score of pre-test is 58.44 and the mean score of post-test is 76.5 The result shows that the mean of post-test is higher than that of pre-test. To analyze the data, the researcher used the t-score formula. After analyzing the data, the researcher found that the value of t-score was 4.058 and the value of t-table at level significance 5% (0.05) was 2.110. From this result, it can be seen that the value of t-score is higher than the value of ttable. It means that the alternative hypothesis (Ha) is accepted and null hypothesis (Ho) is rejected. The conclusion drawn from this study is the implementing authentic assessment through self-assessment in teaching writing hortatory text improves the students’ achievement in writing and yield good result.