The present study aimed to study the diversity of plants used by Phu Thai ethnic groups in Nakhon Phanom province, and to find out the correlation between genders, age, and indigenous knowledge of the Phu Thai groups. The data were analyzed by using independent-samples t-test, one way ANOVA, cultural importance index (CI), informant consensus factor (ICF), and fidelity level (FL %). The results showed that there were 329 plant species from 89 families used in the daily life by the Phu Thai.The largest number of plant species were from Fabaceae (42 species, 12.77 %), followed by Zingiberaceae (20 species, 6.07 %), and Poaceae (15 species, 4.56 %). One hundred and ninety nine species were edible and used for consumption, 176 species for medicine, 56 species for cultural purposes, and 79 for other uses. The highest informant consensus factor (ICF) of medicinal plants were calculated for injuries (ICF = 0.961) indicating the highest degree of agreement among the informants knowledge of medicinal plants used to treat disorders in this category. The highest fidelity level (FL %) values were calculated for Crinum asiaticum L. var. asiaticum (93.62%), showing the conformity of knowledge regarding use of this plant to heal ankle sprains and postpartum women.          The CI values were calculated for Oryza sativa L. (CI = 2.74), followed by Saccharum officinarum L. (CI = 2.64), and Cocos nucifera L. (CI = 2.57), respectively. The most frequently used parts of the plant were leaves (82 species; 21.20 %) followed by fruits (70 species; 17.99 %), and stems (46 species; 11.85 %). Tree was the most common plant habit (77 species; 26.50 %), followed by the herb (72 species; 22.90 %), and climber (34 species; 9.20 %). The plants were gathered from cultivated fields more than from the forest. The ethnobotanical knowledge listed by males and females did not differ significantly (p > 0.05). The older informants had significantly more knowledge of medicinal plant uses than younger informants (p < 0.05). The Phu Thai ethnic group used Oryza sativa L. to make glutinous fermented liquors called “U”. It contains a variety of plants such as Alpinia galangal (L.) Willd., Lepisanthes rubiginosa (Roxb.) Leenh., Albizia myriophylla Benth., Paederia linearis Hook. f. var. linearis, Saccharum officinarum L., Streptocaulon juventas (Lour.) Merr., Oroxylum indicum (L.) Benth. ex Kurz, Harrisonia perforata (Blanco) Merr., and Tacca leontopetaloides (L.) Kuntze.