Background <p>Fibronectin type III domain containing 1 (FNDC1) is a member of fibronectin type III domain protein family, which is known to play an important role in the metastasis of some cancers. However, it has not been reported about the relationship between FNDC1 and ovarian serous cancer.</p> Methods <p>Firstly, we investigated the expression of FNDC1 in various cancer types, and analyzed its diagnostic value and potential role in ovarian serous cancer using TCGA database. Subsequently, a series of bioinformatics methods were used to explore the potential oncogenic effects of FNDC1, including the relationship between FNDC1 expression and immune cell infiltration and immune checkpoint molecules, protein–protein interaction network, gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis, gene set enrichment analysis, and toxicity analysis. Finally, the results were further verified by cell function experiments.</p> Results <p>FNDC1 was highly expressed in ovarian serous cancer, which was further verified in cell line, indicating that it might be as a diagnostic marker of ovarian serous cancer. In addition, the expression of FNDC1 and TNFSF4, an immune checkpoint molecule, showed a strong positive correlation, and both them were involved in the same signaling pathway, indicating that they might jointly affect T-cell responses in ovarian serous cancer. Moreover, this effect might be inhibited by austocystin D.</p> Conclusion <p>FNDC1 was a potential diagnostic marker, prognostic indicator, and target for the treatment of ovarian serous cancer.</p>