Military conflicts between the Kazakhs and the Dzungars were constantly occurring. In particular, the attack of the Dzungars on the Kazakh lands continued until the first half of the 18th century. However, in the battle of Bulanta (1726) and Anirakai (1730), the enemies began to retreat, and the Kazakhs strengthened the troops. In 1745, after the death of the ruler of Dzungars, Galdan Seren, the internal discord between the candidates for the throne worsened, and the foundation of the khanate was destroyed.  Soon after, the Qing Dynasty sent an army and completely destroyed the Dzungars. Those who survived the massacre fled to neighboring khanates. They even reached the Kalmyks along the Volga in order to survive. After the destruction of the Dzungars, direct relations were established between the Kazakh Khanate and the Qing Empire, and in the fall of 1757, Abylay and Abilpeyiz first formed a group of ambassadors and sent them to the royal court in Beijing. Soon, negotiations between the two sides became more frequent, and trade business developed rapidly. In 1758, a trade fair was opened in Urumzhi, and Kazakhs traded horses. Trade markets were opened as soon as Ile (1761) and Shaueshek (1764), which gave a new impetus to the development of the economy of both countries. There are also letters written by Kazakhs in connection with the strengthening of relations between the two countries, which include the letters of Sultan Khanqoja. This article is devoted to the research of the letters sent by Khanqoja Sultan to the Counciller of Tarbaghatai in 1786. In these letters, it is written about the escape and return of Oyirats within the Kazakh border. The language of the letters is foreign, the content is comprehensible, it is considered a very valuable source for studying the social history, language and writing culture of the Kazakh khanate in the 18th century, as well as the Kazakh-Dzungars relationship.