Partial eytochrome oxidase subunits I （COI） and II （COII）, and cytochrome b （Cyt b） genes of thirteen species of the ant genus Formica were sequenced for molecular phylogenetic studies. The sequences were as follows： COI fragment, 657 bp; COl ＋ COIl fragments, approximately 900 bp, including the termination codon at the end of COI and the initiator codon at the beginning of COIl; and the Cyt b fragment, 777 bp. Results show that these three mitoehondrial genetic markers are similar in base composition. The contents of A ＋ T were 73.8% （COl） and 79.2% （COII）--higher than those of G ＋ C, which were 20.8% （COIl） and 26.2% （COI）, and strongly AT-biased. The highest A ＋ T contents were 89.9% （COI） and 93.7% （COII） on the third codon, whereas the lowest G content was 0.2% （COII） and 1.2% （Cyt b）. Molecular phylogenetic trees based on these mitoehondrial genes were reconstructed. Cataglyphis aenescens in the subfamily Formicinae was used as the outgroup, and Diacamma rugosum of the subfamily Ponerinae was used as an additional, distantly-related outgroup. Phylogenetic analysis showed that the differences among the species in the in-group were small, with genetic distance values less than 0.1. The greatest genetic distance was between E beijingensis and F. cunicularia. The results are in accord with those based on morphological features.
