There are 8 normal /a/, /e/, /ı/, /i/, /o/, /ö/, /ö/, /u/, /ü/ and 8 long vowels /aa/, /ee/, /ıı/, /ii/, /oo/, /öö/, /uu/, /üü/ in Altai Turkish. The frequency of use of /aa/, /ee/, /oo/, /öö/, /uu/, /üü/ is wider, while the frequency of use of /ıı/ and /ii/ is narrower, but there are examples where they are used. Altai Turkish has a significant number of long vowel formations that can be analysed in the historical process. Long vowel is expressed by the fact that the articulation time is longer than the normal vowel. Long vowels, which are handled under two headings according to their formation times, are divided into primary (‘original’) and secondary long vowels. Primary long vowels in Altai Turkish did not continue to exist regularly in the historical process like Yakut Turkish and Turkmen Turkish, but in this study, firstly, the examples of primary long vowels that have been preserved from the past to the present, identified as a result of the scanning study from the Altai Turkish dictionary, have been examined. Secondly, it is aimed to determine the existence of secondary long vowels that have formed as a result of contraction in the word structure in Altai Turkish from the Middle Turkish period to the present day, with the vocabulary found in Dîvânu Lugâti't-Türk. The aim of the study is to determine the secondary long vowels formed in the word as a result of contraction in Altai Turkish. The words identified from Altai Turkish Dictionary and Dîvânu Lugâti't-Türk vocabulary has been detected by using diachronic historical study method and scanning method. Keywords: Altai Turkish, Dîvânu Lugâti't-Türk, long vowels, primary long vowels, secondary long vowels.