This qualitative case study explores the impact of Collaborative Digital Storytelling (CDST) on EFL students’ writing skill development at a public university in Central Java. The study aims to investigate (1) Students’ perceptions of their experiences participating in CDST projects, and (2) The specific aspects of writing most improved through the process. Drawing on Vygotsky’s Sociocultural Theory, particularly the concepts of Zone of Proximal Development (ZPD) and scaffolding, the research reveals that CDST provided a socially mediated learning environment where students collaboratively negotiated ideas, co-constructed narratives, and engaged in iterative revision through peer and lecturer feedback. In addition to the sociocultural lens, the study integrates perception theory to highlight both the cognitive and affective dimensions of students’ reflections. Students demonstrated a clear understanding of collaborative strategies and a belief in the effectiveness of peer interaction to improve writing quality. They also expressed positive emotional responses, such as increased interest and motivation, which contributed to their sustained engagement throughout the writing process. Data were collected through open-ended questionnaires and semi-structured interviews with two undergraduate students. The findings indicate that CDST fostered improvements in various writing components, particularly content development, organization, originality, and grammar awareness, while also nurturing students’ awareness, confidence, and emotional investment in writing. The study highlights the potential of CDST to support holistic learning by integrating social, cognitive, and affective processes in EFL writing pedagogy.