Previous Northern blotting analyses of rice seedlings have screened several WRKY genes among the transcripts that are differentially regulated in the following treatments: high salinity, cold stress, polyethylene glycol (PEG) and heat shock. Here, we report characterization of a WRKY gene, OsWRKY08, in rice, which was found to be inducible by PEG NaCl, Abscisic acid (ABA), and naphthalene acetic acid (NAA) as its ortholog AtWRKY28 in Arabidopsis. To determine whether overexpression of OsWRKY08 alters abiotic stress tolerance, 35S::OsWRKY08 recombinant was generated and transformed into Arabidopsis. Physiological tests indicated that 35S::OsWRKY08 transgenic Arabidopsis displayed increased tolerance to mannitol stress through increasing the lateral root number and primary root length during seeding root development. Further, semi-quantitative RT-PCR showed that AtCOR47 and AtRD21, two ABA-independent abiotic stress responded genes, were induced in 35S::OsWRKY08 transgenic plants. These results suggest OsWRKY08 improves the osmotic stress tolerance of transgenic Arabidopsis through an ABA-independent signaling pathway.