In English as a second language (ESL) writing pedagogy, much attention has been given to electronic portfolio (e-portfolio) assessment via social networking sites. However, little is known about how Facebook can be used as an e-portfolio platform. Hence, this paper describes the impact of Facebook-based e-portfolio on ESL students' writing practices and the challenges they encountered in implementing this type of e-portfolio. For this purpose, 171 first-year university students completed a 15-item self-report questionnaire and provided details on the problems they encountered during the e-portfolio implementation. Results indicate that Facebook-based e-portfolio had a positive impact on students' writing practices, making it a viable tool for e-portfolio assessment. Nevertheless, some challenges and suggestions for future implementation were reported. The paper concludes with implications for writing assessment practices and future studies.