Dengue fever, caused by the dengue virus, has been a widespread epidemic during the 21 st century. A mosquito-borne RNA virus, the dengue virus has four serotypes; all are able to cause the disease. Vaccination for the virus is arduous, since the vaccine must be able to immunize all four serotypes. In order to investigate genomic similarities and differences, we analyzed the genomes of the four serotypes: Dengue virus 1, Dengue virus 2, Dengue virus 3, and Dengue virus 4. We investigated the positions on each genome that had significant differences by using the decision tree. We also tried to find the similarities of the four viruses with the apriori algorithm. Through our experiment, we were able to investigate both the genomic similarities and the differences of each serotype, and were able to reach an interesting conclusion that the viruses, though they possess certain similarities, have an unusually large number of differences amongst themselves.