:In this study, we investigated the utility of pentraxin 3 (PTX-3) in bronchoalveolar lavage fluid (BALF) as lung cancer (LCa) diagnostic. A total of 89 LCa patients and 84 non-LCa patients who received bronchoscopy in the First Affiliated Hospital of Xi'an Jiaotong University from December 2014 to February 2015 were enrolled. LCa was subdivided according to pathological type (scale, gland, and small cell lung cancer). BALF samples were obtained during bronchoscopy and PTX-3 levels assayed by ELISA. t-tests, Mann-Whitney, and Kruskal-Wallis tests were performed for the comparison of PTX-3 levels between the different groups. Correlation analysis and receiver operating characteristic (ROC) analysis were used to analyze clinical data. The levels of PTX-3 increased in the LCa groups. PTX-3 levels were higher in the small cell lung cancer (SCLC) compared to non-small-cell lung cancer (NSCLC) groups. In LCa patients, obstructive pneumonia could upregulate the expression of PTX-3 in BALF. The area under the ROC curve of PTX-3 in BALF during LCa diagnosis, SCLC, and LCa with obstructive pneumonia was 0.949 (p ≤ 0.001), 0.672 (p < 0.05), and 0.838 (p < 0.01), respectively. In conclusion, PTX-3 in BALF has a potential value as an LCa biomarker, particularly in cases of SCLC and LCa with obstructive pneumonia.