Rab protein family belongs to the superfamily of ras-like GTP-binding protein. Osrab5B，designated for rab5B gene from rice, encodes a putative Rab protein. In order to investigate the physiological and biochemical functions of this protein OsRab5B, the complete coding sequence (CDS) of Osrab5B was amplified and inserted into a prokaryotic GluGST expression vector, pGEX-4T1, thus constructing the prokaryotic expression vector. The in-frame recombinant plasmid was confirmed by sequencing and was named pG-5BE. Then the vector pG-5BE was transformed into prokaryotic cell E.coli strain BL21 (DE3). The GST fusion protein expressed by this positive strain was purified with GSTrap^TM column. The result from GTP-binding assay proved that the fusion protein has GTP-binding ability.