A cDNA clone (GhUBC1) encoding a ubiquitin-conjugated enzyme (UBC) has been isolated from a cotton ( Gossypium hirsutum L. Cultivar St213) root cDNA library. GhUBC1 encodes a polypeptide of 148 amino acids with a calculated molecular weight of 15 kDa. The GhUBC1 protein is homologous to UBCs found in Arabidopsis thaliana (UBC8), Oryza sativa (UBC), and Saccharomyces cerevisiae (UBC4) and shares amino acid identities of 96%, 90%, and 75%, respectively. The amino acid sequence comparison data suggests that the cotton GhUBC1 is probably involved in the selective degradation of abnormal and short-lived proteins. Northern blot analysis revealed that the GhUBC1 gene is expressed in roots, flowers, and fibers, but with the highest level in the root tissue. Southern genomic blot indicated that two copies of the GhUBC1 gene are present in cotton genome.