Among the Turkic languages the Tuva language possesses the largest number of Mongolian loanwords. This paper tries to prove that unilateral bilinguism played the decisive role in bringing about this phenomenon. The author illustrates the intensity of the Mongolian influence by using linguistic criteria. Then two types of loanwords are presented. The loanwords of the first group were borrowed twice from Mongolian, while in the second group Mongolian loanwords were borrowed despite the fact than an original Turkic word with the same meaning had already existed.