Abstract. Saisor N, Prathepha P, Saensouk S. 2021. Ethnobotanical study and utilization of plants in Khok Nhong Phok forest, Kosum Phisai District, Northeastern Thailand. Biodiversitas 22: 4336-4348. The present study was conducted in Khok Nhong Phok forest, Kosum Phisai District, Maha Sarakham Province, Northeastern Thailand. The forest was surrounded by communities where traditional knowledge has been inherited in the utilization of plants which may disappear over time due to the development of medicinal science and technology. The primary is to study the traditional knowledge in ethnobotanical, collect information about the utilization of plants, and provide the scientific name as the basis for future studies. Data were collected through open-ends interviewing with 30 villagers living in villages around the forest area about their local name, utilization of plants in all 3 aspects, including plants used as food, medicine, and plants used to build houses including parts of plants used. Plant materials and photographs were collected from January to December 2019. Altogether 101 plant species were recorded belonging to 52 families, divided into 3 groups of utilization according to traditional knowledge including 50 species of food plants, 69 species of medicinal plants, and 42 species used for housing, appliances, and fuel. In this study, some plants with more than one type of utilization showed that they were valuable to local people in terms of their uses, and such information can be used as a guideline for the conservation of plant resources in the area to show the importance of cherishing, and maintain valuable resources in the area to remain for future generations.