Abstract: Carbon monoxide (CO) is an important chemical gas messenger molecule in the body with anti-inflammatory activity. As an active substance in gaseous state, the method for its safe and effective delivery towards the lesion sites remains to be established. Based on the natural affinity of carbon monoxide to hemoglobin, a main component of red blood cells (RBCs), this study proposes a carbon monoxide-red blood cell (CO-RBC) composite system, and tested its therapeutic effect against lung injury in an animal model. The mouse model of septic lung injury was adopted, and the carbon monoxide release molecule (CORM-2) was used as a positive control. CO-RBC system was characterized by CO release, stability, toxicity and in vivo lung targeting. The expression of intercellular adhesion molecule (ICAM-1) and pulmonary surfactant protein-A (SP-A) were evaluated in the animal model and the therapeutic effect of CO-RBC system for sepsis was measured by inflammatory factors tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), as well as survival time of mice and pathological changes of the lung. Our results show that CO-RBC system exhibited satisfactory stability with negligible CO release during 48 h storage under nitrogen protection, while the CO release was about 70% within 12 h under physiological condition, in contrast to CO burst release from CORM-2. The CO-RBC system showed no significant toxicity in the animal model, and in vivo fluorescence imaging results showed effective accumulation in the lungs, supporting its lung targeting effects. The secretion of TNF-α and IL-6 in the CO-RBC group was significantly lower than that in other groups, the degree of pulmonary interstitial edema was relieved, the white blood cell infiltration was decreased, and the survival rate was significantly improved. Therefore, the CO-RBC system has a significant inhibitory effect on the pulmonary inflammatory response in septic mice compared with CORM-2. This system provides a new hope for therapeutic treatment of sepsis.