Ras homolog enriched in brain (Rheb) belongs to a small GTPase superfamily,the Ras superfamily,which regulates diverse cellular functions such as neural plasticity and cell cycle,by modulating its GTP or GDP-bound status in animals,plants and microorganisms.Bombyx mori Rheb (BmRheb) gene is composed of 549 bp which encodes 182 amino acids.BmRheb was constructed into a modified pET-28a(+) vector and expressed successfully in E.coli BL21 (DE3) cells.The recombinant BmRheb was purified with Ni2+-chelating affinity chromatography followed by a Superdex 75 column.Gel filtration analysis showed that the purified recombinant protein existed in dimer and tetramer states in solution,which was in accord with other small GTPases previous reported.The Circular Dichroism (CD) results indicated that the α-helix structures of BmRheb was almost completely wrecked at 50 ℃,suggesting BmRheb was extremely sensitive to temperature.RT-PCR results showed that BmRheb was expressed highly in tissues including malpighian tubule,ovary,testis and silk gland in the fifth instar day 3 larvae,implying BmRheb may be involved in multiple processes such as silk synthesis,cell cycle.These results may be helpful to study the functions of BmRheb during the development of silkworm in the future.