Proliferating cell nuclear antigen (PCNA) is an essential protein for both DNA replication and DNA repair. In the present study using two-hybrid analysis with PCNA from rice, Oryza sativa L. cv. Nipponbare (OsPCNA), we found that OsPCNA interacted with rice DnaJ protein. We have identified DnaJ and designated it as OsDnaJ. OsDnaJ was able to bind to OsPCNA in vitro. Transcripts of OsDnaJ were found to be strongly expressed in the proliferating cells. mRNA of DnaJ was induced by UV and DNA-damaging agents such as H2O2. The expression patterns of OsPCNA were almost the same as OsDnaJ. The relationship between OsPCNA and OsDnaJ is discussed.