P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are classified as the non-coding RNA group and are 26–30 nt long. Unlike other small RNAs, piRNAs originate from long single-stranded primary transcripts. In this review, the structures, biogenesis process, and main functions of piRNAs are explained, and new findings regarding the role of piRNAs in ovarian cancer (OC) are focused on. Altering piRNA expressions may be a ssociated with ovarian cancer oncogenesis, and piRNAs associated with ovarian cancer pathways can be used as prognostic biomarkers or target therapeutics. PiRNAs have promising potential in diagnosis and targeting several diseases including OC. Investigating the correlation between piRNA expression and treatment responses will enable the use of piRNAs for personalized OC treatment in the future.