ATL31, an Arabidopsis RING-type ubiquitin ligase, plays a critical role in plant carbon/nitrogen (C/N)-nutrient responses during post-germinative growth and in defense responses to pathogen attack. ATL31 expression under these stress conditions suggested the presence of transcriptional regulators mediated by these stress signals. We recently reported that the expression pattern of WRKY33, a transcription factor involved in plant defense responses, is highly correlated with that of ATL31. In this study, we investigated the detailed relationship between the ATL31 gene and WRKY33. Using transient reporter analysis, we found that WRKY33 could significantly activate ATL31 transcription in plant cells. Transcript analysis of stable transgenic Arabidopsis plants overexpressing WRKY33 confirmed that the expression of ATL31 in response to the PAMPs flg22 and chitin was enhanced compared with wild-type plants, while expression was repressed in wrky33 mutants. Further detailed transient reporter analysis revealed that transactivation by WRKY33 is required and mediated through a specific W-box cis-acting element in the promoter region of the ATL31 gene. In contrast, WRKY33 did not regulate ATL31 expression during the C/N response. Taken together, these results demonstrate that WRKY33 acts as a transcription factor of ATL31 and positively regulates its expression during activation of plant defense responses.