Context: Cancer-related pain is associated with significant suffering and is one of the most challenging symptoms to manage. Studies indicate that front-line clinicians often lack the knowledge on best practices in cancer pain management. Objectives: The current project, a quality improvement (QI) initiative, evaluated the outcome of an online educational intervention for nurses on complex cancer pain management. Methods: An online 7-module educational intervention, Advanced Pain Assessment and Management, was offered from 2012 to 2017. Pre-post course evaluations included self-reported knowledge and confidence across cancer pain management domains. In-course competency assessments included knowledge examination, online discussion forum participation, opioid dosage calculation assignment, and small-group-based case study. A mixed-model statistical analysis was used to assess pre-post course change in pain management confidence level. Results: In all, 306 nurses from 89 hospitals in Ontario, Canada, were enrolled in the course; 81.4% returned the precourse survey and 71.9% successfully completed the course. The average confidence level on pain management was low at baseline (57.5%) but improved significantly post-course. Incourse competency assessments ranged from 81% to 89%. Mixed-model results showed post-course improvements in confidence levels, independent of sociodemographic background, clinical role, and professional educational level. Nurses with longer years of practice and more cancer cases reported greater confidence. Conclusion: A facilitator-led online educational intervention focusing on complex cancer pain management can significantly improve nurses' knowledge, confidence, and skills. Low baseline knowledge among nurses highlights the pressing need for health-care organizations to implement cancer pain management training as an integral part of health-care QI initiative.