The study of “Aquatic Plants in Ethno-medicinal Uses of Sitamarhi District, Bihar (India)” was conducted to document the available medicinal plants and their traditional applications among the local people from 2018 to August 2019 in Sitamarhi District of Bihar. Purposive sampling method was used to select traditional medicinal practitioners of the study area. A semi-structured questionnaire was prepared and personal interviews were conducted to gather firsthand information about ethno-medicinal plants. The highest numbers of plants were used for Skin problems followed by respiratory diseases, skeletomuscular diseases and dental problems. Local people are still playing a great role in the primary health care system of Sitamarhi District. Some practitioners were ensuring the 100% results of their formulations against many serious diseases. The plant specimens were deposited in the herbarium of Central Library, Babasaheb Bhimrao Ambedkar Bihar University Muzaffarpur, Bihar, India.