The Wilms' tumor gene WT1 is overexpressed in various tumors, and the WT1 protein has been demonstrated to be an attractive target antigen for cancer immunotherapy. A WT1 protein-derived 16-mer peptide, WT1332 (KRYFKLSHLQMHSRKH), which was naturally generated through processing in cells and could elicit Th1-type CD4+ helper T cell responses with an HLA-DRB1*0405-restriction has previously been identified by us. In the present study, it has been demonstrated that WT1332 can induce WT1332-specific CD4+ T cell responses with the restriction of not only HLA-DRB1*0405 but also HLA-DRB1*1501, -DRB1*1502, or -DPB1*0901. These HLA class II-restricted WT1332-specific CD4+ T cell lines produced IFN-γ but neither IL-4 nor IL-10 with WT1332 stimulation, thus showing a Th1-type cytokine profile. Furthermore, HLA-DRB1*1501 or -DRB1*1502-restricted WT1332-specific CD4+ T cell lines responded to WT1-expressing transformed cells in an HLA-DRB1-restricted manner, which is consistent with our previous finding that WT1332 is a naturally processed peptide. These results indicate that the natural peptide, WT1332, is a promiscuous WT1-specific helper epitope. WT1332 is expected to apply to cancer patients with various types of HLA class II as a WT1-specific helper peptide in combination with HLA class I-restricted WT1 peptides.