Self-assessment as one of authentic assessments has been currently implemented in EFL teaching pedagogy as to give more opportunity to the students to reflect on their own learning and progress. This study aims at investigating the effect of self-assessment on students' independence and writing competence. In the present study, two groups of junior secondary school students in Indonesia were investigated in their learning of English due to the use of self-assessment towards their independence and writing competence of three genre texts. The research used a post-test only control group design in which one group was given an experimental treatment using self-assessment, while the other received a conventional assessment utilizing teacher's assessment. There were two types of instruments used, questionnaire of students' independence and writing competence test which underwent validity and reliability testing beforehand. The data were analyzed using a one-way ANOVA and MANOVA. Before the inferential statistics analyses were conducted, the data were pre-requisitely tested in terms of normality, homogeneity, and multi co-linearity. The results prove that self-assessment has an effect on the students' independence and writing competence. Thus, teachers are recommended to promote the use of self-assessment to improve the students' independence and writing competence.