The nucleic acid-binding protein Purα is involved at stalled DNA replication forks, in double-strand break (DSB) DNA repair and the cellular response to DNA replication stress. Purα also regulates homologous recombination-directed DNA repair (HRR). We investigated the effects of the DNA damage-inducing cancer chemotherapeutic agent cisplatin on mouse embryo fibroblasts (MEFs) from PURA-/- knockout mice that lack Purα. Cells lacking Purα showed enhanced sensitivity to cisplatin as evaluated by assays for cell viability and cell clonogenicity. This was seen both in Purα-negative MEFs and in human glioblastoma cells treated with siRNA directed against Purα. MEFs lacking Purα also showed enhanced H2AX phosphorylation in response to cisplatin. Repair of a reporter plasmid that had been treated with cisplatin was decreased in a reactivation assay using Purα-negative MEFs and the capacity of nuclear extracts from Purα-negative MEFs to perform non-homologous end-joining in vitro was also impaired. Purα has a role in the cellular response to cisplatin-induced DNA damage and may provide new therapeutic modalities for cisplatin-resistant tumors.