Collagen type IV (Col IV) is the main constituent of the basement membrane. Under physiological conditions, Col IV plays an important role in maintaining epithelial integrity and stabilizing epithelial function of the gastric mucosa. Under pathological conditions, Col IV can be free from the basement membrane under the influence of tumor cells and play a pro-metastatic role. Although there is a increasing number of investigations on Col IV, no studies to date have directly uncovered the prognostic role and potential regulatory role of the six isoforms of Col IV in gastric cancer. In the present experiment, we aimed to analyze the role of COL4A family genes in gastric cancer. COL4A1/2/3/4 was significantly overexpressed, while COL4A5/6 was decreased in gastric cancer tissues according to TCGA data and our immunohistochemical staining results. And COL4A1 had a positive correlation with tumor stage, while COL4A5/6 had negative correlations with tumor stage. COL4A1/2/4/5/6 can be considered as a diagnostic indicator of gastric cancer. High levels of COL4A1/2/4/5/6 expression may be predictive of a poor prognosis of gastric cancer. The percentages of genetic alterations in COL4As for stomach cancer varied from 3 to 17% based on the TCGA data (COL4A1, 10%; COL4A2, 8%; COL4A3, 3%; COL4A4, 5%; COL4A5, 17%; COL4A6, 17%). Besides, COL4As may modulate tumor progression by participating in classical cancer pathways: COL4A1/2/3/4/5/6 can activate the EMT process; COL4A2/3/4/6 can inhibit apoptosis and cell cycle; COL4A3/4/5 can activate the PI3K/AKT signaling pathway. This study implied that COL4As have diagnostic and prognostic value for gastric cancer.