The recent release of the domestic dog genome provides us with an ideal opportunity to investigate dog-specific genomic features. In this study, we performed a systematic analysis of CpG islands (CGIs), which are often considered gene markers, in the dog genome. Relative to the human and mouse genomes, the dog genome has a remarkably large number of CGIs and high CGI density, which is contributed by its noncoding sequences. Surprisingly, the dog genome has fewer CGIs associated with the promoter regions of genes than the human or the mouse. Further examination of functional features of dog-human-mouse homologous genes suggests that the dog might have undergone a faster erosion rate of promoter-associated CGIs than the human or mouse. Some genetic or genomic factors such as local recombination rate and karyotype may be related to the unique dog CGI features.