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Polo-like kinase 1 (Plk1), a serine–threonine kinase, plays a key role in the regulation of the cell cycle. Elevated Plk1 expression in various cancers is correlated with poor prognosis and poor patient survival rates. Several Plk1 inhibitors are currently being developed as potential treatments for cancer. In the present study, we investigated whether dendritic cells (DC) electroporated with mouse Plk1RNA (mPlk1RNA/DC) can induce Plk1-specific immune responses and exert antitumor effects in various murine tumor models. Overexpression of Plk1 protein was confirmed in several mouse and human tumor cell lines and various cancer tissues. Furthermore, Plk1-specific CD4+ and CD8+ T cells were induced by vaccination with mPlk1RNA/DC and the cytotoxic activity of the T cells was demonstrated against several Plk1-expressing tumor cell lines. Vaccination with mPlk1RNA/DC inhibited the growth of MC-38 and B16F10 tumors in C57BL/6 mice and the growth of CT26 tumors in BALB/c mice. Depletion of CD8+ T cells reversed the inhibition of tumor growth by mPlk1RNA/DC vaccination. Homologous human Plk1RNA-electroporated DC also inhibited tumor growth in MC-38 tumor-bearing mice. In addition, Plk1-specific cytotoxic T lymphocytes from PBMC of healthy donors could be induced using autologous monocyte-derived DC electroporated with RNA encoding the whole gene of human Plk1. Taken together, the results of the present study suggest that Plk1 could be a universal tumor antigen recognized by cytotoxic T lymphocytes for cancer immunotherapy. (Cancer Sci 2011; 102: 1448–1454)