Ubiquitin, the small conserved protein, is present in most types of tissues in eukaryotes. In their structure, ubiquitin genes have two forms: polyubiquitins and ubiquitin extension protein genes (also known as ubiquitin fusion genes). Each species has at least one polyubiquitin locus containing the tandem repeats of ubiquitincoding monomer containing 228 bp for 76 amino acids. The number of tandem repeats can vary between loci within species and between species. Ubiquitin involves in proteolysis recognizing denatured proteins and polypeptides, or polypeptides need to be removed through the specific ubiquitination by the ubiquitinproteasome system. There are three types of enzymes involved in this process: ubiquitin-activating enzyme E1
ubiquitin-conjugating enzyme E2 and ubiquitin-ligating enzyme E3 (E3 ligase). The ubiquitination regulates many protein function in cells, plays an important role in the growth and development of plants as well as disease resistance and tolerance to different stresses in the environment. The diversity of functions of ubiquitin has created the permission to use the ubiquitin promoter as an effective constitutive promoter in plant genetic engineering. The promoters showed higher level of gene expression in plants than CAMV35S promoter in times. For monocots this lever has been higher than that in dicotyledonous plants. In this article, the knowledge about ubiquitins, the assumption of their functions, the encoding genes and the subsequent isolation and characterisation of ubiquitin promoter, prospects of their application in plant genetic engineering will be analyzed and discussed.