Studies have suggested that micro-RNAs (miRNAs) can function as an oncogene or a tumor suppressor in cancers. However, the role of MIR-138-5P (613394) in prostate cancer (PCa) remains unclear.,Expression level of MIR-138-5P in PCa cell lines and normal cell line was analyzed with the quantitative real-time PCR method. Cell counting kit-8 assay, colony formation assay, wound-healing assay, and transwell invasion assay were performed to analyze the biological functions of MIR-138-5P.,We showed MIR-138-5P expression level was significantly decreased in PCa cell lines compared with the normal cell line. Overexpression of MIR-138-5P inhibits PCa cell proliferation, colony formation, cell migration, and cell invasion in vitro. Mechanistically, we showed Forkhead box C1 (FOXC1, 601090) was a direct target for MIR-138-5P in PCa. We confirmed that overexpression of FOXC1 partially reversed the effects of MIR-138-5P on PCa cell behaviors.,Collectively, we showed that MIR-138-5P functions as a tumor suppressor gene in PCa via targeting FOXC1.,© 2020 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.