Background <p>Palliative care (PC) is essential for improving the quality of life of patients with chronic and life-limiting illnesses, yet PC education remains inconsistent across medical curricula. In Türkiye, where structured PC rotations and hospice training are limited, medical students often graduate with gaps in foundational PC knowledge, particularly in oncology. This study evaluated the impact of a brief, online, oncology-focused PC module and assessed long-term knowledge retention after graduation.</p> Methods <p>In a controlled experimental design, 150 sixth-year medical students were enrolled into intervention and control groups. The intervention group completed a single online educational session consisting of three instructional modules covering PC principles, cancer-specific applications, pain management, symptom control, and psycho-oncological support. Knowledge was measured using a de novo 20-item assessment tool developed to address common misconceptions within the Turkish medical context. A partial-credit scoring system captured both correct knowledge and uncertainty. Participants were re-assessed two years after graduation using matched identification codes. Statistical analyses included independent-samples t tests, Mann–Whitney U tests, chi-square tests, Holm-adjusted subscale comparisons, effect size estimation, and multivariable logistic regression to explore predictors of high-re-test performance.</p> Results <p>Post-test knowledge scores were significantly higher in the intervention group compared with controls (<i>p</i> &lt; 0.001), with large effect sizes. Improvements were most pronounced in understanding PC definitions, principles, and the scope of cancer-related PC. Although pain management showed gains, misconceptions persisted, reflecting broader trends in the literature. At the two-year re-test, knowledge remained higher among intervention participants (<i>p</i> &lt; 0.01). In multivariable logistic regression, higher post-test scores and being a general practitioner, likely reflecting broader patient exposure in primary care, were significant predictors of strong long-term performance. Completer-only sensitivity analyses confirmed the robustness of findings.</p> Conclusion <p>Even brief, targeted online training can meaningfully improve medical students’ understanding of palliative care, with knowledge gains sustained well into early clinical practice. In settings where formal PC rotations are limited, structured online modules offer a feasible approach to strengthening early PC education. Integrating such modules with clinical observation and interdisciplinary learning may further enhance competence and has the potential to better prepare future healthcare professionals for the complex needs of patients with life-limiting illness.</p>