The study of plant diversity in Mueang District, Nakhon Ratchasima Province is important for biodiversity conservation and for the area to become a protected area for the plant genetic conservation project. Fifteen plots were used for this preliminary study, between March and September 2015, in mixed deciduous forest of Mueang Mai Kokkruat Subdistrict Municipality. Fifty-five families, 77 genera, and 125 species were found. Common families were Fabaceae, followed by Malvaceae, Phyllanthaceae, Euphorbiaceae, Apocynaceae, and Rubiaceae. Dominant tree species were Lagerstroemia spp., Atalantia monophylla (L.) DC., Cratoxylum cochinchinense (Lour.) Blume, Lannea coromandelica (Houtt.)Merr., and Bauhinia saccocalyx Pierre. Common species of understory plants were Helicteres lanata (Teijsm. & Binn.) Kurz, Evolvulus alsinoides (L.) L., Sida acuta Burm.f., Tephrosia purpurea (L.) Pers., and Ruellia tuberosa L. This research provides basic information for further study. The data also provides the conservation criterion to preserve species richness and is useful for the long term study of natural resources