<![CDATA[The integration of Education for Sustainable Development (ESD) into English Language Teaching (ELT) has become increasingly important in preparing students to respond to complex global challenges. However, empirical evidence regarding the effectiveness of SDG-themed Project-Based Writing in developing both sustainability awareness and academic writing competence among EFL learners remains limited. This study investigates the effect of SDG-themed Project-Based Writing on environmental sustainability awareness and academic writing performance among undergraduate EFL students. A pre-experimental one-group pretest–posttest design was employed involving 42 students enrolled in an Academic Writing course at an Indonesian university. Data were collected using an Environmental Sustainability Awareness Questionnaire and an analytic academic writing rubric assessing text organization, coherence and cohesion, language accuracy, academic resource use, and argumentation quality. Data were analyzed using descriptive statistics, paired-samples t-test, Wilcoxon Signed-Rank Test, and Cohen’s d effect size analysis. The findings revealed a significant improvement in students’ sustainability awareness (t(41) = −5.95, p < .001, |d| = 1.119), with the largest improvement occurring in sustainability knowledge. Academic writing performance also improved significantly (Z = −5.651, p < .001, |d| = 1.585), particularly in academic source utilization, text organization, and argumentation quality, whereas language accuracy showed minimal change. These findings indicate that SDG-themed Project-Based Writing provides an effective pedagogical approach for integrating sustainability education with EFL academic writing development.]]>
