The iUUCD is a comprehensive ubiquitin and ubquitin-like conjugation database for 148 species from fungi, plants to animals (Ensembl release version 87). We classified all 68 animals into 11 categories including primates, rodents, laurasiatheria, afrotheria, xenarthra, metatheria, birds & reptiles, amphibians, fishes, other chordates and other animals according to Ensembl taxonomy. Users could click the names on the left treeview or small logos on the right picture of phylogenetic tree to browse each species. Users could also Browse by species of plants or Browse by specise of fungi.