Cold stress adversely affects plant growth and crop production. Some plants express a series of cold-responsive genes during cold acclimation to reduce the damage of cold stress. Among them, transcription factors play important roles in enhancing plant cold tolerance. A bHLH-type gene OsbHLH1 was isolated from rice. The predicted OsbHLH1 protein has a putative nuclear-localization signal and a putative DNA binding-domain bHLH-ZIP. The genomic sequence of the OsbHLH1 gene is unique in rice genome and has four introns. The transcription of the OsbHLH1 gene was specifically induced in roots of rice seedlings by cold but not by NaCl, PEG and ABA treatments. The OsbHLH1 protein was located in the nucleus of plant cells and had the ability to activate the transcription of the reporter gene in yeast. In addition, OsbHLH1 had the ability to dimerize. These results indicate that the OsbHLH1 may function as a transcription factor in a cold signal-transduction pathway.