This paper addresses the only known linguistic data on Yöröö Khamnigan Ewenki—an innovative dialect of Ewenki once spoken along the Yöröö River in Selenge province, Mongolia. The Mongolian Tungusologist L. Mishig undertook brief fieldwork in 1963 among the Yöröö Khamnigan, and published his field notes on the language in a short article (Mishig 1968). His article contains the only known data on this unique variety of Ewenki. The primary goal of this article is to bring this data to the attention of scholars outside of Mongolia, and to present modern linguistic analyses of the largely unanalyzed data contained in Mishig’s article. I supplement these analyses with findings from my 2009 salvage fieldwork in Yöröö county, Selenge province, seeking out remaining speakers or rememberers of the language.