Quantitative analysis of dopamine (DA) in body fluids is essential owing to its close relation to some nervous system diseases. However, there are still significant challenges in exploring new materials with good sensitivity and biocompatibility for real-time medical monitoring. Herein, we developed the nano-MnO₂-modified red blood cell (RBC@MnO₂), a novel whole-cell electrochemical biosensor for detecting DA. The n-MnO₂ grown in situ on the cell surface can increase the transmembrane electron transfer rate and electrochemically active surface area of the catalyst. The as-prepared biosensor exhibits a high sensitivity (11.73 μA·μM⁻¹·cm⁻²), a low detection limit (0.068 μM), and a wide linear range (0.6–160 μM) toward DA detection, which can be applied for DA detection in real-time health monitoring in whole blood samples with satisfactory results.