Small ubiquitin-like modifiers (SUMOs) are structurally related to ubiquitin and are ligated to lysine residues within sumoylation target proteins. Currently, a growing body of evidence shows that the SUMO family has evolved as an important modifier of many proteins in a variety of cellular pathways. In this study, we have cloned cDNA encoding for three different pig SUMO isoforms. The full-length cDNA encoding for pig Sumo1, Sumo2 and Sumo4 consists of 306, 288 and 288 nucleotide base pairs of the open reading frame, respectively, and the putative amino acid sequences of pig Sumo1, Sumo2 and Sumo4 are composed of 101, 95 and 95 peptides, respectively. The structures of pig SUMOs are evolutionally well conserved, and their expression has been detected in a broad range of tissues. We also determined that all pig SUMOs are localized within the nucleus. However, the different tissue expression observed in individual pig SUMOs may show the divergent or specialized role of each of the pig SUMO isoforms. Future studies will focus on the identification of targets for sumoylation by different pig SUMO isoforms and the analysis of the functional consequences of sumoylation during the course of infectious diseases in pigs.