Insects and animals can recognize surrounding environments by detecting thousands of chemical odorants. Olfaction is a complicated process that begins in the olfactory epithelium with the specific binding of volatile odorant molecules to dedicated olfactory receptors (ORs). OR proteins are encoded by the largest gene superfamily in the mammalian genome. We report here the whole genome analysis of the olfactory receptor genes of S. scrofa using conserved OR gene specific motifs and known OR protein sequences from diverse species. We identified 1,301 OR related sequences from the S. scrofa genome including 1,113 functional OR genes and 188 pseudogenes. OR genes were located in 46 different regions on 16 pig chromosomes. We classified the ORs into 17 families, three Class I and 14 Class II families, and further grouped them into 349 subfamilies. We also identified inter- and intra-chromosomal duplications of OR genes residing on 11 chromosomes. A significant number of pig OR genes (n=212) showed less than 60% amino acid sequence similarity to known OR genes of other species. We also performed a similar analysis on the cattle OR subgenome and identified 1,071 OR related sequences. We show that S. scrofa has one of the largest OR repertoires, suggesting an expansion of OR genes in the swine genome. Considering available information from literature, it seems that OR systems between mammals and insects possess high similarity in their action mechanisms and rapid evolutionary changes due to differences in living environments.