MicroRNAs (miRNAs) are short, endogenous non-coding RNA molecules involved in cancer initiation and progression. Using transwell migration and invasion assays, we found that miR-631 inhibited the migration and invasion of prostate cancer (PCa) cells. Bioinformatic algorithms indicated the 3'-untranslated region (3'-UTR) of zeta-associated protein 70 (ZAP70) has a putative binding site for miR-631. We found that miR-631 can bind to the 3'-UTR of ZAP70 and decrease its expression. Further studies confirmed that ZAP70 facilitates PCa cell migration and invasion. Interestingly, using gain- and loss-of function experiments, we found that ZAP70 is a major target of miR-631 and largely mediates its activity. In addition, we further discovered that miR-631 was downregulated and ZAP70 was overexpressed in PCa cell lines and PCa tissues. A concordant inverse correlation between miR-631 and ZAP70 was also found in PCa tissues. In all, our study demonstrates that miR-631 decreases PCa cell migration and invasion by dampening ZAP70 expression. (C) 2015 Elsevier Inc. All rights reserved.