Poly (ADP-ribosyl)ation (PARylation) plays a crucial role in DNA replication, particularly during S phase, where it is detected at replication sites on the lagging strand to facilitate Okazaki fragment processing. However, the role of dePARylation in DNA replication remains elusive. In this study, we demonstrate that poly (ADP-ribose) glycohydrolase (PARG) is actively involved in degrading poly (ADP-ribose) at DNA replication sites during S phase. Inhibition of PARG in S-phase cells leads to the accumulation of DNA single-strand breaks at replication sites. Furthermore, suppression of dePARylation during S phase impairs DNA replication, which can be rescued by wild-type PARG but not by a catalytically inactive PARG mutant. Mechanistically, we show that PCNA, a key factor in DNA replication, is PARylated by PARP1 during S phase, which reduces its interaction with FEN1. Timely removal of PARylation from PCNA by PARG restores the interaction between PCNA and FEN1, thereby facilitating DNA replication. Taken together, our findings reveal that PARG promotes DNA replication through the dePARylation of PCNA during S phase, highlighting the critical role of PARG in DNA replication.© 2025 The Author(s). The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.