OBJECTIVE： To investigate clinical significance of programmed cell death 5 （PDCD5） protein in serum of patients with lung cancer. METHODS： 80 lung cancer inpatients were selected from the First Affiliated Hospital of Shihezi University School of Medicine （hereinafter referred to as “our hospital”） as lung cancer group； 60 healthy volunteers were selected from our hospital at the same period as normal group. ELISA was used to test the expression of PDCD5 protein， and the relationship of PDCD5 protein with clinical pathological features of lung cancer patients were analyzed. RESULTS： The expression of PDCD5 protein in normal group was significantly higher than lung cancer group， with statistical significance （P＜0.05）. The expression of PDCD5 protein in lung caner patients was not associated with gender， smoking history and pathological type （P＞0.05）； it was decreased as the decrease of tumor differentiation degree， with statistical significance （P＜0.05）. The expression of PDCD5 protein in patients with carcinoembryonic antigen （CEA）＜5.6 μmol/L was significantly higher than those with CEA≥5.6 μmol/L； the expression of PDCD5 protein in patients with cytokeratin 19 soluble fragment （CYFRA21-1）＜5.6 μmol/L was significantly higher than those with CYFRA21-1≥5.6 μmol/L， with statistical significance （P＜0.05）. The expression of PDCD5 protein in patients with Ⅰ-Ⅱstage lung cancer was significantly higher than Ⅲ-Ⅳ stage lung cancer patients； the expression of PDCD5 protein in patients without distant metastasis was significantly higher than those with distant metastasis. The expression of PDCD5 protein was in decreasing as the increase of the number of metastasis site， with statistical significance （P＜0.05）. CONCLUSIONS： PDCD5 protein in serum of patients with lung cancer shows low expression level， which is related to tumor differentiation degree， tumor marker level as CEA and CYFRA21-1， tumor stage and distant metastasis， etc. The detection of PDCD5 protein may contribute to clinical diagnosis of lung cancer.