DNA polymerase beta (pol beta) is a key player in DNA base excision repair (BER). Here, we describe the complex formation of pol beta with the protein arginine methyltransferase 1 (PRMT1). PRMT1 specifically methylated pol beta in vitro and in vivo. Arginine 137 was identified in pol beta as an important target for methylation by PRMT1. Neither the polymerase nor the dRP-lyase activities of pol beta were affected by PRMT1 methylation. However, this modification abolished the interaction of pol beta with proliferating cell nuclear antigen (PCNA). Together, our results provide evidence that PRMT1 methylation of pol beta might play a regulatory role in BER by preventing the involvement of pol beta in PCNA-dependent DNA metabolic events.