Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis, which has been implicated in the pathogenesis of fibrotic lung diseases, including idiopathic pulmonary fibrosis (IPF). The aim of this study was to examine the clinical significance of the serum VEGF level for evaluating disease severity and progression. The levels of VEGF in serum were measured in 41 patients with IPF, 14 patients with lung cancer, and 43 healthy volunteers. We measured the serum levels of CRP, LDH, KL-6, SP-D, and the parameters obtained from arterial blood gas analysis and pulmonary function tests. High-resolution computed tomography (HRCT) was performed to determine the extent of the interstitial and the alveolar opacities. The ability of each biomarker to predict disease severity was estimated by measuring the area under the receiver operating characteristic curve (AUC). The VEGF levels of IPF patients with high alveolar-arterial difference of oxygen (AaDO(2)) levels were significantly elevated than those with low AaDO(2) levels and those of healthy volunteers. When examined within the IPF group, a significant positive correlation was found between the VEGF levels and the HRCT interstitial score (p = 0.027) and the KL-6 levels (p = 0.037). Among several serum biomarkers, VEGF showed the largest AUC for predicting disease severity as defined by a high AaDO(2) value. There was an inverse correlation between the baseline VEGF level and the monthly change in percent predicted vital capacity. The serum VEGF level may reflect the severity of IPF and offer clinical benefits to predict the disease's progression.