The Arabidopsis Jasmonate ZIM-domain proteins (JAZs) act as substrates of SCF(COI1) complex to repress their downstream targets, which are essential for JA-regulated plant development and defense. The bHLH transcription factor MYC2 was found to interact with JAZs and mediate JA responses including JA-inhibitory root growth. Here, we identified another bHLH transcription factor MYC3 which directly interacted with JAZs by virtue of its N-terminal region to regulate JA responses. The transgenic plants with overexpression of MYC3 exhibited hypersensitivity in JA-inhibitory root elongation and seedling development. The JAZ-interacting pattern and the JA-induced expression pattern of MYC3 were distinguishable from those of MYC2. We speculate that MYC3 and MYC2 may have redundant but also distinguishable functions in regulation of JA responses.