This paper provides a constraint-based analysis of the syllable structure of onset consonant sequences in Najdi Arabic, spoken in central Saudi Arabia. Unlike Classical or Standard Arabic, Najdi is believed to allow consonant clusters in the onset. The study tested two assumptions. The first is that Najdi onset clusters result from a vowel deletion process, leading to different kinds of clusters with distinct sonority hierarchies and that these form complex onsets. The second is that Najdi inputs are different from Classical or Standard Arabic, in which there is no vowel in the underlying representation and hence no deletion occurs, resulting in simplex onsets. The paper adopted optimality theory to analyze the data, considering a phenomenon that occurs in the speech of Najdi speakers. Following this framework, constraints were utilized to demonstrate the syllable structure of the onset clusters in Najdi according to the above assumptions. The results revealed consonant sequences rather than consonant clusters, meaning the consonants were not parsed in the same syllable, agreeing with previous acoustic research.