J-domain proteins, with a molecular mass of around 40 kDa, are a family of proteins that contain a signature J or J-like domain. Serving as co-chaperones of Hsp70s, J-domain proteins play critical roles in nascent protein folding, maintaining of correct protein conformations, translocation of proteins across cellular membranes, degradation of misfolded proteins, and assembly and disassembly of protein complexes. Due to great progresses have been made in J-domain proteins of plants, this review briefly introduces the structure and classification of J-domain proteins, mainly highlights their functional roles and action mechanisms in plants, and finally gives a prospect of this field.