The long non-coding RNA PVT1 reportedly forms a circular RNA variant (circPVT1). As circPVT1 is expressed in various cancers and has been implicated in promoting cancer cell proliferation and tumor progression, it is considered a potential biomarker and therapeutic target. We previously confirmed that circPVT1 expression varies according to the Gleason pattern, a morphological indicator of malignancy in prostate cancer. In this study, we assessed the expression of circPVT1 using BaseScope^TM assay with prostate cancer tissues and evaluated the correlation with the Grade Group (based on Gleason pattern), an indicator used to morphologically evaluate the degree of malignancy of prostate cancer. The relationship between circPVT1 expression and tumor proliferation was evaluated using cells in which circPVT1 expression was suppressed using the clustered regularly interspaced short palindromic repeats (CRISPR)/RfxCas13d system. BaseScope^TM assay confirmed that circPVT1 expression was significantly higher in Grade Group 2–5 (intermediate- and high-grade groups) than Grade Group 1 (low-grade group). In vitro experiments using the CRISPR/RfxCas13d system showed that specific suppression of circPVT1 expression resulted in a significant reduction in the number of prostate cancer cells. The results of this study suggest that circPVT1 is involved in tumor growth in prostate cancer and may serve as a therapeutic target for moderately and highly malignant prostate cancers that express circPVT1.