Abstract: The plant hormone auxin regulates many processes of plant growth and development as well as environmental adaptation, including embryonic development, organogenesis, and tropism. To perform these functions, auxin mainly depends on the typical TIR1/AFB-auxin-Aux/IAA-ARF signaling pathway. In this pathway, the canonical Aux/IAA proteins which are composed of four conserved domains play a key role in auxin signaling as co-receptor with TIR1/AFB. Recently, it has been found that some non-canonical Aux/IAA proteins lacking conserved domain(s) are also involved in the auxin response. This review focuses on the research advances of non-canonical Aux/IAA proteins from the aspects of protein structure, biological function and auxin signal transduction, and finally discusses and prospects the future research directions of these proteins.