Background: Back pain caused by prolonged bed rest is a common complication following Percutaneous Coronary Intervention (PCI) via femoral access, which can decrease patient comfort and delay recovery. Purpose: To determine the effectiveness of early mobilization in reducing back pain among post-PCI patiens. Method: This study employed a randomized controlled trial (RCT) design with a pretest-posttest control group approach and was conducted from March to April 2026 at Murni Teguh Hospital in Medan. The sampling technique used was random sampling, with a sample size of 66 participants divided into an intervention group and a control group. The independent variable in this study was early mobilization, while the dependent variable was the level of back pain. Data analysis included univariate analysis in the form of frequency distributions and bivariate analysis using the Wilcoxon Signed-Rank Test, the Mann-Whitney Test, and multiple linear regression. Results: The median pain score in the intervention group decreased from 6 to 0, whereas the control group remained at a median score ogf 6. There was a statiscally significant difference in pain reduction between the two groups (p=0.000) with a large effect size (r=0.800). Multivariate analysis identified early mobilization as the most influential factor associated with back pain reduction. Conclusion: Early mobilization is an effective and safe evidance-based nursing intervention for reducing back pain in post-PCI patients. Keywords: Back Pain; Cardiovascular; Early mobilization; Percutaneous Coronary Intervention (PCI).