Ovarian cancer is one of the most common gyneacologic malignancies, with high morbidity and high mortality. Hsa-miR-122-5p (miR-122) has been reported with tumor-suppressing roles in various cancers. In this study, miR-122 was overexpressed in ovarian cancer cells, and phenotypic experiments demonstrated that miR-122 inhibited migration and invasion in SKOV3 and OVCAR3 cells. MiR-122 also suppressed epithelial mesenchymal transition (EMT), evidenced by expression changes of E-cadherin, vimentin, matrix metalloproteinase (MMP)2, and MMP14. Prolyl-4-hydroxylase subunit alpha-1 (P4HA1) was identified as a target of miR-122, and downregulated by miR-122. MiR-122-induced the elevation of migration, invasion, and EMT were recovered by P4HA1. Additionally, miR-122 restrained the tumor metastasis of SKOV3 cells in peritoneal cavity of nude mice. In summary, we demonstrated that miR-122 inhibited migration, invasion, EMT, and metastasis in peritoneal cavity of ovarian cancer cells by targeting P4HA1 for the first time, which shed lights on the discovery of miR-122 and P4HA1 as possible potential diagnostic markers and therapeutic targets for ovarian cancer.