Objective To evaluate the diagnostic value of monocyte chemokine-1(MCP-1)and CD40 ligand(CD40L)levels in patients with bronchiectasis(BE)complicated with pulmonary infection.Methods A total of 94 patients with BE complicated with pulmonary infection who received treatment in Department of Geriat-rics in the hospital from March 2021 to March 2023 were included as the BE complicated infection group.Ac-cording to the Clinical Pulmonary Infection Score(CPIS),they were divided into severe infection group(17 cases).moderate infection group(52 cases).and mild infection group(25 cases).Another 94 cases of BE with-out pulmonary infection were selected as the BE group.94 healthy people who underwent the physical exami-nation during the same period in the hospital were selected as the control group.The distribution of pathogenic bacteria in BE patients complicated with pulmonary infection was analyzed.The levels of serum MCP-1 and CD40L in each group were compared.Receiver operating characteristic(ROC)curve was applied to analyze the diagnostic value of serum MCP-1 and CD40L in BE complicated with pulmonary infection.Results Total-ly 99 strains of pathogenic bacteria were isolated from 94 BE patients complicated with pulmonary infection.Among them,73 strains(73.74％)were Gram-negative bacteria,mainly Klebsiella pneumoniae.17 strains(17.17％)were Gram-positive bacteria,mainly Staphylococcus aureus.9 strains(9.09％)were fungal strains,mainly composed of Candida albicans.The serum levels of MCP-1 and CD40L in the BE combined with infec-tion group were obviously higher than those in the BE group and the control group(P＜0.05).The levels of serum MCP-1 and CD40L in the severe infection group and the moderate infection group were obviously high-er than those in the mild infection group(P＜0.05),and the serum levels of MCP-1 and CD40L in the severe infection group were obviously higher than those in the moderate infection group(P＜0.05).The area under the curve of the combined diagnosis of serum MCP-1 and CD40L for BE complicated with pulmonary infection was larger than that of the single detection(Z combination-MCP-1=2.896,P=0.005,Zcombination-CD40L=4.547,P＜0.001),with sensitivity of 91.49％and specificity of 76.60％.Conclusion The levels of serum MCP-1 and CD40L in patients with BE complicated with pulmonary infection are elevated,which could be used to assess the severity of pulmonary infection,and the combination of the two has high diagnostic value for BE compli-cated with pulmonary infection.