R2* mapping is an emerging biomarker to evaluate iron overload. Due to its relative insensitivity to motion, free-breathing 3D stack-of-radial imaging is a useful technique in patient populations with breath-hold difficulties. However, its performance for R2* quantification is still under investigation. This study proposes a new 3D self-gating motion-compensated free-breathing stack-of-radial MRI method for R2* quantification. Preliminary in vivo results demonstrated good agreement of R2* mapping in the liver with the proposed method compared to the reference results of breath-hold Cartesian MRI.