Rwanda and Burundi were two countries in one, Ruanda-Rundi, which displayed an exceptional single language, Rwanda-Rundi also known as Kinyarwanda-Kirundi. In 1962, both countries became independent as two separate countries, Rwanda and Burundi, with two different languages, Kinyarwanda and Kirundi. This paper aimed at assessing the powerful influence that Kinyarwanda exerted over Kirundi without the reverse. This study was conducted in Rwanda to Burundians Living in Rwanda and some Rwandese who had ever lived in Burundi, face-to-face with conversation with questionnaire, and telecommunication with phone and voice recording. The main findings revealed that, among the 140 informants who effectively responded in this study, the 57 informants approximately 40.7% were examined affected. More the language increasingly rated in use more it dominated and controlled. At the end of this paper, all readers would walk away with a full understanding about how Kinyarwanda the main language spoken mainly in Rwanda, influenced on Kirundi the main language of Burundi. Both issued governmental sides should intervene in this case in order to care of saving and defending the origin languages.