Objective <p>To evaluate the effect of nurse-led shared decision-making support based on a decision aid on decisional conflict among patients with pulmonary nodules, and to explore its effects on psychological distress, satisfaction with participation in decision-making, and pulmonary nodule-related knowledge.</p> Methods <p>The intervention group received nurse-led shared decision-making support using a decision aid in addition to physician treatment recommendations, whereas the control group received standard care. Decisional conflict, psychological distress, satisfaction with participation in decision-making, and pulmonary nodule-related knowledge were assessed immediately after the intervention (T1), at 3 months (T2), and at 6 months (T3). Causal-steps mediation analysis was conducted to examine the mediating effects of pulmonary nodule-related knowledge and satisfaction with participation in decision-making. Generalized estimating equations were used to analyze longitudinal differences between groups.</p> Results <p>A total of 98 patients were enrolled, including 47 in the intervention group and 51 in the control group. The intervention group had a significantly lower decisional conflict score than the control group after the intervention (22.87 ± 17.49 vs. 48.02 ± 19.93; <i>t</i> = 6.58, <i>p</i> &lt; 0.001). The intervention group also had significantly higher scores for satisfaction with participation in decision-making and pulmonary nodule-related knowledge than the control group (both <i>p</i> &lt; 0.001). Mediation analysis showed that shared decision-making support significantly reduced decisional conflict (B = −25.05, 95% CI −32.74 to −17.36), and this effect was mediated by improvements in pulmonary nodule-related knowledge and satisfaction with participation in decision-making. Longitudinal analysis showed that psychological distress decreased more rapidly in the intervention group during follow-up, with significant between-group differences at T1 and T2 (<i>p</i> &lt; 0.001).</p> Conclusion <p>Nurse-led shared decision-making support based on a decision aid reduced decisional conflict among patients with pulmonary nodules when integrated into routine clinical care. This effect was mainly mediated by improvements in pulmonary nodule-related knowledge and satisfaction with participation in decision-making. The intervention also showed beneficial effects in reducing psychological distress during follow-up.</p> Trial Registration <p>The study was registered in the Chinese Clinical Trial Registry on March 20, 2023(ChiCTR2300069553, retrospectively registered).</p>