Abstract: Objective To determine the value of galactomannan (GM) in bronchoalveolar lavage fluid (BALF) for diagnosing invasive pulmonary aspergillosis. Methods According to the European Organization for Research and Treatment of Cancer / Invasive Fungal Infection Group (EORTC / IFICG) and the American Mycosis Research Group (MSG), and the American College of Infectious Diseases (IDSA) guidelines, 295 patients with pulmonary aspergillosis (IPA) and high risk of invasive infections were divided into four groups: IPA group (42 cases), clinically diagnosed group (68 cases), suspected group (61 cases), and non-IPA group (124 cases). Their serum and BALF concentrations of GM were detected by enzyme-linked immunosorbent assay (ELISA).The clinically diagnosed and confirmed invasive pulmonary fungal infections (IPFI) were treated as golden standards (+). A GM value ≥ proposed threshold was deemed diagnostic test positive. Receiver operating characteristic (ROC) curves were drawn to determine the diagnostic efficiency of BALF GM assay for IPFI. The optimal cut-off point of BALF GM was determined using Youden index. Results BALF GM had an area under the curve (AUC) of 0.932 in diagnosing IPFI, with 87.5% sensitivity,96.7% specificity, 87.5% positive predictive value, and 96.7% negative predictive value when the BALF GM value was set at 1.5 ng/mL as the optimal cut-off point. Higher BALF and serum GM values were found in the confirmed IPA group, followed by the clinical diagnosed group compared with the non-IPA group (P<0.05). The threshold value was set at 0.5 ng/mL for serum GM and 1.5 ng/mL for bronchoalveolar lavage GM. Higher positive rates were found in the confirmed IPA group and the clinical diagnosed group compared with the non-IPA group (P<0.05). Serum GM appeared to have higher false positives and false negative rates. Conclusion BALF GM is a rapid and accurate indicator with high sensitivity and specificity for the early diagnosis of IPA.