This study determined the knowledge of aetiology of Onchocerciasis among the Inhabitants of Riverine Areas in Southeast Nigeria. The study was guided by eight research questions and six null hypotheses. Descriptive survey design was used and the population of the study consisted of 4,177,828 of inhabitants in Anambra State and 3,927,563 of inhabitants of riverine areas in Imo State. The sample consisted of 1,200 inhabitants of the riverine areas in Anambra and Imo state selected using multi-stage procedure. The instruments for data collection Knowledge of the aetiology for Oncherciasis (KOAO). Research questions 1 and 2 were answered using Aggregate scores. frequencies and percentages were used to answer research questions, Chi-Square, statistics were used to test the hypotheses. The results showed that majority of the in Anambra and Imo states riverine inhabitants have knowledge of the aetiology of Onchocerciasis. The following recommendations were made among others: There should be Community-based Campaigns on the knowledge and preventive strategies of Onchocerciasis for the Inhabitants of Riverine areas. Development of Health Education materials should focus on the epidemiological information in other to ensure better understanding of individuals risk perception to the disease as far as they are living in the riverine areas. Awareness Campaign should be intensified among the Riverine areas in other to educate the people on Onchocerciasis occurrence and prevention.