One of the general tendencies among the world languages is that of avoiding vowel hiatus in the phonetic level. One of the vowel hiatus strategies is changing the second vowel into a glide. This article tries to analyze a case in Kalhori Kurdish based on Harmonic Serialism, and reviews the main concepts in the Optimality Theory. In Kalhori Kurdish, if one of the low vowels comes before a high vowel, the latter changes into a glide so as to avoid vowel hiatus; and if the former is low front some changes come into play. The main aim of the article is the order of some of the relevant universal constraints in Kalhori Kurdish in a way to justify the derivation of glide forms from the URs. In the end, the article comes up with the contraints' order *VV, MAX LEX, DEP >> MAX [+low] >> AGREE (GLIDE) >> IDENT.
