BACKGROUND: New graduate registered nurses (NGRNs) working in the Intensive Care Unit (ICU) face challenges translating theoretical knowledge into clinical practices, especially within the informal learning environment. This study explored NGRNs' experiences with informal learning and its role in addressing complex clinical scenarios. METHODS: Utilizing Interpretive Phenomenological Analysis (IPA) as its foundational philosophy and methodology, this research employed semi-structured interviews to reveal NGRNs' learning processes. RESULTS: NGRNs primarily relied on observation and practice, questioning and communication, and feedback during shift changes. These strategies were crucial for their professional development, contributing to skill acquisition, establishing work patterns, and gaining independent working capabilities. However, limitations of informal learning could lead to inconsistent experiences with knowledge and potential patient safety risks. CONCLUSION: Informal learning is vital for NGRNs' professional development but requires structured support and guidance to ensure patient safety and improve care quality. Managers and educators should create an open, flexible environment for questioning and consultation and enhance educator's feedback skills. High transitional stressors and workload can undermine NGRNs' motivation to continue learning after reaching an advanced beginner level. Future efforts should develop effective interventions to overcome obstacles in informal learning pathways, improving NGRNs' learning efficiency and quality.