ABSTRACT. MYB, v-myb avian myeloblastosis viral oncogene homolog, proteins play central roles in plant stress response. Previously, we identified a novel R2R3-MYB transcription factor, GmMYB12B2, which affected the expression levels of some key enzyme genes involved in flavonoid biosynthesis in transgenic Arabidopsis. In the present study, we analyzed the expression levels of GmMYB12B2 under salt, low temperature, drought, abscisic acid (ABA), and ultraviolet (UV) radiation treatments in soybean using semi-quantitative reverse transcription polymerase chain reaction. The expression of GmMYB12B2 was drastically induced by UV irradiation and salt treatment, but no response was detected under low temperature, drought, and ABA stresses. A detailed characterization of the GmMYB12B2 overexpression lines revealed that GmMYB12B2 might be involved in response of plants to UV radiation and salt stresses. Transgenic Arabidopsis lines constitutively expressing GmMYB12B2 showed an increased tolerance to salt and UV radiation treatment compared with wild-type plants. The expression levels of certain salt stress-responsive genes, such as DREB2A and RD17, were found to be elevated in the transgenic plants. These results indicate that GmMYB12B2 acts as a regulator in the plant stress response.