Kaposi's sarcoma-associated herpesvirus (KSHV) encoded ORF59 plays an essential role in viral lytic replication by providing DNA processivity activity to the viral DNA polymerase, ORF9. ORF59 forms a homodimer in the cytoplasm, binds and translocates ORF9 into the nucleus where it secures ORF9 to the origin of lytic DNA replication (oriLyt) in order to synthesize long DNA fragments during replication. ORF59 binds to the oriLyt through an immediate early protein, replication and transcription activator (RTA). Here, we show that viral kinase, ORF36, phosphorylates serines between 376-379 of ORF59 and alanine substitution of Ser378 residue had significantly impaired phosphorylation. Although mutating these serine residues had no effect on binding between ORF59 and ORF9, viral polymerase or ORF36, the viral kinase, it significantly reduced the ability of ORF59 to bind with RTA. Alanine substitution mutant of Ser376-379 showed that both Ser378 and 379 contribute to binding with RTA Additionally, Ser376, Ser378, and Ser379 residues were critical for binding of ORF59 to oriLyt and its processivity function. Ablation of these phosphorylation sites reduced the production of virion particles, suggesting that phosphorylation is critical for its activity and viral DNA synthesis.