AIM: To evaluate effects of inhaled nitric oxide(iNO) on adhesion molecule CD11b expression on lung neutrophils in experimental meconium aspiration syndrome(MAS) rabbits treated with conventional mechanical ventilation under room air or 100%O 2. METHODS: Animals were randomly allocated to 8 groups( n= 48) of 6 each: two MAS model groups(under room air or 100%O 2 without iNO treatment), 6 treatment groups were treated with continuous NO inhalation at a dose of 0.2?10 -6 mol/L,0.33?10 -6 mol/L or 0.67?10 -6 mol/L respectively for 12 hours under room air or 100%O 2. Mean systemic arterial pressure(SAP) and methemoglobin (MeHb) were performed at basement time, 0, 2, 4, 12 hours. Expression of CD11b on neutrophils in the bronchoalveolar lavage fluid(BALF) was detected with flow cytometry. RESULTS: SAP, MeHb at different time among different groups were within the normal scale. CD11b expression on the neutrophils in the BALF significantly decreased in groups of inhalation 0.33?10 -6 mol/L or 0.67?10 -6 mol/L NO, compared with the two MAS model groups. ( ?s : under 21%O 2, 0.33?10 -6 mol/L NO,121?20 vs 392?204; 0.67?10 -6 mol/L NO,112?30 vs 392?204;under 100%O 2,0.33?10 -6 mol/L NO,113?24 vs 293?65; 0.67?10 -6 mol/L 102?114 vs 293?65, P 0 05). No statistic difference was observed between groups inhaled 0.33?10 -6 mol/L NO and 0.67?10 -6 mol/L NO. CONCLUSION: 0.33?10 -6 mol/L or 0.67?10 -6 mol/L NO inhalation down-regulated the CD11b expression on the neutrophils in BALF to reduce the sequestration of neutrophils in rabbit lung.