Placenta-specific protein 1 (PLAC1), a placenta-specific gene, is known to be involved in the development of placenta in both humans and mice. However, the precise role of PLAC1 in placental trophoblast function remains unclear. In this study, the localization of PLAC1 in human placental tissues and its physiological significance in trophoblast invasion and migration are investigated by technical studies including real-time RT-PCR, in situ hybridization, immunohistochemistry, and functional studies by utilizing cell invasion and migration assays in the trophoblast cell line HTR8/SVneo as well as the primary inducing extravillous trophoblasts (EVTs). The results show that PLAC1 is mainly detected in the trophoblast columns and syncytiotrophoblast of the first-trimester human placental villi, as well as in the EVTs that invade into the maternal decidua. Knockdown of PLAC1 by RNA interference significantly suppresses the invasion and migration of HTR8/SVneo cells and shortens the distance of the outgrowth of the induced EVTs from the cytotrophoblast column of the explants. All the above data suggests that PLAC1 plays an important role in human placental trophoblast invasion and migration.