DNA polymerase gamma (Polγ) is a nuclear encoded, mitochondrially located replicase that conducts all DNA synthesis in the organelle. Structurally, human Polγ closely resembles bacteriophage T7 DNA polymerase. Perhaps due to this prokaryotic-like feature, Polγ is highly susceptible to inhibition by drugs designed against HIV reverse transcriptase and HCV RNA polymerase. Mutations on Polγ have been implicated in human diseases affecting muscular, neurological and endocrine systems. I will summerize our recent structural and biochemical studies towards understanding Polγ-mediated antiviral drug toxicity, and the molecular basis for certain diseases.