BACKGROUND The Miao people in Hainan possesses a profound historical heritage and unique ethnic culture. Through centuries of confronting survival challenges in tropical rainforest mountains, they have accumulated abundant knowledge of disease prevention and treatment. However, the traditional medicinal knowledge of the Hainan Miao people has been scarcely documented to date. This ethnobotanical study aims to: (1) record Miao people's traditional medicinal knowledge; (2) analyze medicinal properties and threats; (3) put forward suggestions for promoting the development of traditional medical knowledge of the Miao people. METHODS From 2020 to 2022, 35 key informants (Miao healers, local herbalists, and plants gatherers, age range is 30-99 years) were interviewed in 11 regions of Hainan by means of participatory observation, semi-structured interview, key informant interview, and group discussion. The quantitative analysis employed the use value (UV), informant consensus factor (ICF), relative frequency of citation (RFC), and similarity index (Cj). The International Classification of Primary Care-2nd (ICPC-2) was used to classify the diseases treated by medicinal plants. RESULTS A total of 348 medicinal plant species belonging to 114 families were recorded. These were primarily herbaceous plants (37.71%), with leaves (48.85%) most used, and decoction (39.94%) most frequently employed. Among them, 37 medicinal plants documented in this study were recorded for their medicinal value for the first time, enriching the database of medicinal plant resources. These plants are used to treat 140 different diseases, which can be categorized into 14 disease categories, primarily focusing on the treatment of musculoskeletal (L), respiratory (R), and digestive (D) disease with medicinal plants. The informant consensus factor (ICF) values for these categories are 0.55, 0.51, and 0.5, respectively. In addition, the use value (UV) values of Stephania succifera and Sarcandra glabra are relatively high. Plantago asiatica, Imperata cylindrica, Homonoia riparia, and Aquilaria sinensis had high relative frequency of citation (RFC) values, between 0.05 and 0.16. Furthermore, the Hainan Miao and the Li ethnic groups exhibit a high degree of similarity in their use of medicinal plants due to their similar living environments and the inheritance of traditional medicinal knowledge. In contrast, compared to the Guizhou Miao ethnic group, significant differences arise due to the differing geographical environments and living habits. CONCLUSIONS This demonstrates that through oral transmission and personal instruction, knowledge of medicinal plants diversity has been passed down from generation to generation, ensuring its continuity and preserving a unique traditional culture for treating various diseases. However, the aging of knowledge holders poses a threat to the loss of traditional knowledge, making it imperative to take measures to preserve the continuity of this knowledge. This survey provides valuable data and insights for the sustainable utilization and conservation of Miao medicinal plant resources, as well as the transmission of traditional medical knowledge.