This study was conducted to explore the effects of genre-based writing instruction on thesis proposal writing self-efficacy and writing quality. Twenty-two graduate students majoring in Teaching English as a Foreign Language participated in the study. Drawing on Bandura's (2006) guidelines, we developed a proposal writing self-efficacy questionnaire, which students completed at the beginning of the semester and the end of one semester. They wrote a preliminary proposal at the beginning of the semester, that is, before being exposed to a genre-based approach. For one semester the students’ awareness was raised concerning the generic structures of the sections included in the thesis proposal and relevant lexico-grammatical features were highlighted. Students initially showed strong writing self-efficacy, which significantly increased at the end of the semester. They also showed remarkably significant improvement in their proposal writing skills. Students’ pre-instruction skills perception was higher than their proposal quality, which may be attributed to their lack of knowledge of academic writing conventions. However, after receiving genre-based instruction, their proposal quality surpassed their level of self-efficacy. The results of this study are discussed, and implications of the study are provided.