Increasing evidences have proved that circular RNAs (circRNAs), identified as a specific kind of non-coding RNAs, play a potential critical role in tumorigenesis including prostate cancer. However, the function of circRNAs in human prostate cancer remain largely unknown. In this study, we demonstrated that the expression of circZMIZ1 was higher in plasma of human prostate cancer than the paired benign prostatic hyperplasia (BPH) patients' plasma. Moreover, in cultured prostate cancer cells, knockdown of circZMIZ1 inhibited cell proliferation and caused cell cycle arrest at G1. Mechanistically, we also showed that circZMIZ1 could increase the expression of androgen receptor (AR) and androgen receptor splice variant 7 (AR-V7), which may be partly contributed to the occurrence and development of prostate cancer. In conclusion, these results revealed that circZMIZ1 might serve as a novel biomarker and a treatment target for prostate cancer treatment.