Abstract: A portion (the big intron between exon 5 and 6, ca. 2 kb) of glycerol-3-phosphate acyltransferase (GPAT) gene of 15 wild tree peony accessions collected from 15 populations, which represent all the eight wild species in sect. Moutan, was analyzed using PCR-RFLP technique, and this portion of nine accessions, which represent also all the eight wild species, was sequenced for a better understanding of the interspecific relationships in this section. A reduced-median (RM) network of sect. Moutan was constructed with Network 3.0 computer program using the PCR-RFLP data obtained from the digestion experiments of 12 selected restriction enzymes. Both maximum parsimony (MP) and neighbor-joining (NJ) trees of sect. Moutan were constructed with PAUP*4.0 program using the sequences newly obtained in this study and from GenBank. As a result, a well resolved and highly supported gene tree of sect. Moutan (by bootstrap values) was obtained. The tree is basically in accordance with that constructed from morphological data. The phylogenetic relationships among species in sect. Moutan are discussed in detail.