New evidence suggests that microRNAs (miRNAs) play an important role in regulating the development and progression of prostate cancer. However, their specific functions and mechanisms remained to be further explored. MiR-129 has been reported in gastric cancers, colon cancer and lung cancer. In this study, we disclosed a new tumor suppresser function of miR-129 in prostate cancer. The purpose of our study is to clarify the effects of miR-129 in cellular processes correlated with cancer development and progression of prostate cancer cell by regulating ETS1. MiR-129 and ETS1 expression in prostate cancer tissues, tumor adjacent tissues and cells were tested by quantitative real-time PCR. We validated the target relationship between miR-129 and ETS1 by dual luciferase reporter gene system. MTT, colony formation, tumorigenesis assays, flow cytometry, wound healing and transwell assays were used to analyze cell viability, proliferation, migration, and invasiveness in vivo and in vitro. The level of ETS1 protein expression was detected by western blot. Here we demonstrate that miR-129 have a relatively reduced expression in prostate cancer cell lines and tissues. Morever, the miR-129 inhibits the expression of ETS1 by binding its 3′-UTR. The overexpression of miR-129 can inhibit PC-3 cell viability, proliferation, migration and invasion through targeting ETS1 by PI3K/AKT/mTOR signaling pathway. These findings suggested that miR-129 could directly suppress ETS1, which might be one of potential mechanisms in inhibiting cell processes including viability, proliferation, migration and invasiveness of prostate cancercells and it provides new clues for us to understand the carcinogenesis of prostate cancer. In addition, it may help to develop a treatment approach for ETS1-activated prostate cancer.