With the development of tourism at home and abroad, Rapeseed (Brassica napus) has become an important ornamental plant. However, its ornamental value at the inflorescence stage is greatly reduced by Sclerotinia sclerotiorum. Identification of important genes in the defense responses is critical for molecular breeding, which is an important strategy for controlling the disease. In this study, we isolated a B. napus WRKY transcription factor gene, BnaWRKY75. BnaWRKY75 was found to encode a nucleus-localized protein and exhibited relatively high expression in the stems. Arabidopsis thaliana transgenic plants expressing BnaWRKY75 showed enhanced resistance to S. sclerotiorum, and both ProBnaWRKY75:GUS and gene expression analyses showed that BnaWRKY75 was highly responsive to S. sclerotiorum infection, indicating the involvement of BnaWRKY75 in response to this infection. Furthermore, overexpression (OE) of BnaWRKY75 in B. napus significantly enhanced the resistance to S. sclerotiorum, whereas the resistance was reduced in RNAi transgenic B. napus plants. Moreover, the BnaWRKY75-OE B. napus plants exhibited constitutive activation of salicylic acid-, jasmonic acid-, and ethylene-mediated defense responses and the inhibition of both H₂O₂ and O₂^.- accumulation in response to this pathogen. By contrast, BnaWRKY75-RNAi plants showed a reverse pattern, suggesting that BnaWRKY75 is involved in hormonal signaling pathways and in the control of reactive oxygen species accumulation. In conclusion, these data indicate that BnaWRKY75, a regulator of multiple defense responses, positively regulates resistance against S. sclerotiorum, which may guide the improvement of resistance in rapeseed.