This paper seeks to show how the optimality theory regulates the syllabification of Standard Arabic, in general, and Najdi Arabic in particular. The arrangement of phonemes in the syllables is ruled by constraints. This paper shows how Najdi Arabic repairs the words adopted from Modern Standard Arabic to conform to Najdi Arabic constraints. The data is adopted from different sources such as previous studies, and the researcher’s own data. Although a number of studies have been conducted on Arabic, this is the first study that implements the optimality theory to account for Najdi Arabic syllabic structure. Issues tackled here include epenthesis, syncope, the markedness of sonority hierarchy, vowel shortening, cluster tolerance and apocope. The analysis here is conducted at the word level.