Unrelieved cancer pain has an adverse impact on quality of life. While routine screening and assessment forms the basis of effective cancer pain management, it is often poorly done, thus contributing to the burden of unrelieved cancer pain. The aim of this study was to test the impact of an online, complex, evidence-based educational intervention on cancer nurses' pain assessment capabilities and adherence to cancer pain screening and assessment guidelines. Specialist inpatient cancer nurses in five Australian acute care settings participated in an intervention combining an online spaced learning cancer pain assessment module with audit and feedback of pain assessment practices. Participants' self-perceived pain assessment competencies were measured at three time points. Prospective, consecutive chart audits were undertaken to appraise nurses' adherence with pain screening and assessment guidelines. The differences in documented pre-post pain assessment practices were benchmarked and fed back to all sites post intervention. Data were analyzed using inferential statistics. Participants who completed the intervention (n = 44) increased their pain assessment knowledge, assessment tool knowledge, and confidence undertaking a pain assessment (p< .001). The positive changes in nurses' pain assessment capabilities translated into a significant increasing linear trend in the proportion of documented pain assessments in patients’ charts at the three time points (χ2 trend = 18.28, df = 1,p< .001). There is evidence that learning content delivered using a spaced learning format, augmented with pain assessment audit and feedback data, improves inpatient cancer nurses' self-perceived pain screening and assessment capabilities and strengthens cancer pain guideline adherence.