Peroxisomes (microbodies), one of the subcellular organelles, have been shown to have indispensable functions in the metabolism of n-alkanes, fatty adds, methanol, and several nitrogen-containing compounds in eukaryotic microorganisms after we described the appearance of large numbers of the organelles in an n-alkane-assimilating yeast, Candida tropicalis. It has been suggested that peroxisomes proliferate by division from already existing peroxisomes and their characteristic proteins, which are encoded by nuclear genes, have been shown to be specifically localized after synthesis outside peroxisomes. These physiological phenomena can be controlled simply by changing the carbon and/or nitrogen source for growth, making microorganisms an excellent target to investigate the biogenesis of peroxisomes in eukaryotic cells. This article deals with the functions of peroxisomes in alkane metabolism by yeasts, together with discussion about the mechanisms of their development and degradation as well as the properties and application of peroxisomal enzymes.