GRAS proteins, named after the first three members GAI, RGA and SRC, has been found in 294 embryophyta species and is represented by 1,035 sequences. They belong to a plant-specific protein family and play essential roles in plant growth and development. Proteins in this family are defined as minimally containing a conserved GRAS domain, which is about 350-450 resides and can be subdivided into five distinct motifs with their name derived from the most prominent amino acids: LRI (leucine-rich region I), VHIID, LRII (leucine-rich region II), PFYRE and SAW and mainly function in the interaction between GRAS proteins and their partners (Sun et al., 2012).By phylogenetic analysis, the GRAS family can be divided into more than ten subfamilies, of which SCL4/7 is one important subgroup and functions in response to environmental stresses. Here we describe a detailed protocol for the expression and purification of the GRAS domain of Os-SCL7, a SCL4/7 member in rice, which enables us to crystallize it and determine its structure.