This article presents the research of the recently discovered Mansi dictionary rewritten by A.M. Shegren from the Pallas archive. The uniqueness of this source lays in the fact that its data do not correspond to any known dialects but has lexical similarities with the Mansi dialect spoken along the Berezovo river. In order to clarify the dialectical identity of this dictionary we had a detailed analysis based on the Proto-Mansi reconstruction and the material of the modern Mansi dialects. Also, this archival material was analyzed from the point of the dialectal differentiating isoglosses. The research indicated that the language of that new dictionary has a number of characteristics which are absent in other Mansi dialects.