The dehydration responsive element binding protein 2 (DREB2) subgroup belongs to the plant-specific APETALA2/ethylene-responsive element binding factor (AP2/ERF) family of transcription factors. We have characterized cDNA encoding Arabidopsis thaliana DREB2C, which is induced by mild heat stress. Both an electrophoretic mobility shift assay (EMSA) and a yeast one-hybrid assay revealed that DREB2C(145-528) was able to form a complex with the dehydration responsive element/C-repeat (DRE/CRT; A/GCCGAC) motif. A trans-activating ability test in yeast demonstrated that DREB2C could effectively function as a trans-activator. Constitutive expression of DREB2C under the control of the cauliflower mosaic virus (CaMV) 35S promoter led to enhanced thermotolerance in transgenic lines of Arabidopsis. Microarray and RT-PCR analyses of transgenic plants revealed that DREB2C regulates expression of several heat stress-inducible genes that contain DRE/CRT elements in their promoters. From these data, we deduced that DREB2C is a regulator of heat stress tolerance in Arabidopsis.