Currently, the palaeopteran lineages (insect orders Ephemeroptera and Odonata) that have a problematic relationship with neopteran lineages are poorly represented by mitogenome sequences. In this study, we have determined the complete mitogenome of the oriental mayfly, Ephemera orientalis (Ephemeroptera: Ephemeridae), and the dragonfly Davidius lunatus (Odonata: Gomphidae). The 16 463 bp mitogenome of E. orientalis and the 15 912 bp mitogenome of D. lunatus have many of the features typically detected in insect mitogenomes. Although the initiation codon for the D. lunatus COI gene is the typical ATA, E. orientalis is unusual in that no typical start codon was detected in the start region of the COI gene. The A+T-rich regions of both mitogenomes have some unusual features. The E. orientalis A+T-rich region harbors two identical 55 bp sequences separated by 158 bp, and the D. lunatus A+T-rich region harbors a tandem repeat comprising two identical 261 bp copies and one partial copy of the repeat. Additionally, the A+T-rich regions of both mitogenomes harbor the stem-and-loop structures flanked by the conserved sequences "TA(A)TA" at the 5' end and "G(A)nT" at the 3' end, which have been suggested to be the signals involved in minor strand replication initiation. Furthermore, the D. lunatus A+T-rich region contains two tRNA-like structures with proper anticodon and cloverleaf structures.