The ubiquitinproteasome system (UPS) plays an important role in posttranslational process, which is responsible for a diverse array of biologically important cellular processes. The UPS is also involved in the protein quality control, which maintains the health of the cell. Thus, the UPS provides a clue for understanding of the molecular mechanisms underlying various tolerances of organism to diversiform adverse conditions as well as stress combination. Ubiquitinconjugating enzyme (E2) is a critical component of UPS. Cloning of ubiquitinconjugating enzyme gene (PyE2) of Porphyra yezoensis Ueda will facilitate us to investigate tolerance of P. yezoensis to diversiform adverse conditions and degradation of enable protein by UPS. cDNA sequence (GenBank accession: FJ232910) of PyE2 was isolated successfully through experiment of RT-PCR under direction of in silico cloning. This cDNA contained a 444 nt of complete open reading frame (ORF) coding a 16.6 ku protein (PyE2) of 147 amino acids sequence. PyE2 had significant amino acid sequence identity and similarity with E2s from other organism, which indicated E2 was highly conserved in the evolution. PyE2 contained conserved sequence and cysteine residue of active site of E2 family, and tertiary structure of PyE2 was similar to human class I E2. PyE2 was a class I member of E2 family of P. yezoensis according to bioinformatics analysis.