This article classifies and analyzes the assimilation words expressed in masnavi “Gulshan ul-asror” of Haydar Khorezmi’s, one of the mature representatives of our classical literature, who lived and worked in Khorezm in the late XIV and early XV centuries. It is natural that the interaction, neighborliness and trade relations of peoples of different languages have an impact on the development of their languages, first of all, on their vocabulary. As a results, there are cases of exchange and assimilation. In general, it is expedient to analyze foreign words in the lexicon of Turkic languages by dividing them into two groups:1) ancient (pre-Islamic) period which Sanskrit, Sogdian and Chinese elements are specific;2) relatively new (Islamic and post-Mongol) period. This group includes Arabic, Persian-Tajik and Mongolian dialects. In this study, we examine the pre-Islamic state of the lexemes of the assimilation layer mentioned in the Masnavi. The emergence of Sugd, Sanskrit and Chinese assimilation words in the vocabulary of Turkic languages is assessed as a product of the close ties of the Turkic peoples with the Sughd, Indian, Chinese and Khorezm peoples since ancient times.