This article deals with the issues concerning structural-phonetic transformations of diphthongs and separate sound complexes within words of Iranian origin in such Turkic languages of Central Asia as Kyrgyz, Kazakh, Uzbek and Uighur. The languages of the ethnic groups that inhabited the territories of contemporary Central Asia have since ancient times developed in close connection with Iranian languages, namely the Perso-Tajik literary language. It should be noted that in the process of borrowing the words of Iranian origin have been subjected to certain phonetic regularities, which in turn served as a mechanism for their adaptation in Turkic languages, which is explained by the diversity of the Turkic and Iranian languages in their structural-typological features. However, the phonetic transformation of the phonetic complexes in the Iranian lexical borrowings in the Kyrgyz, Kazakh, Uzbek, Uighur languages, as well as in their dialects occurred differently, despite the genetic relationship of the above mentioned languages.