Fatty acids are the major components of membrane molecules. The fact that unsaturated fatty acids play multiple important roles, physically and biologically, means that the ratio of unsaturated to saturated fatty acids in the membrane needs to be strictly regulated to maintain cellular homeostasis. The most ubiquitous and widespread modification to fatty acids, which results in a great diversity of different structures, is the insertion of double bonds. Fatty acid desaturases directly introduce regioselective double bonds into fatty acids. A phylogenetic analysis of desaturases suggests that the sequences of these proteins include a highly conserved domain, which determines the differences in specificity and regioselectivity found in these enzymes. In this study, we performed a systematic analysis of fatty acid desaturases found in the genomic data of 397 organisms. We obtained a set of desaturases clustered by regioselectivity using a hierarchal clustering analysis.