Optimality theory (OT) is the latest model of phonology which views the language acquisition process as a way of reordering universal constraints provided by Universal Grammar (UG) according to the language-specific grammar. It, therefore, presents a more promising model towards language universalities. This study aims to utilize the OT framework to provide a deep comprehensive analysis of syllable types and stress assignment system of Standard Arabic (SA). To achieve the purpose of the study, mono-syllabic, di-syllabic, tri-syllabic and quadrisyllabic words taken from SA were analyzed. Since SA is a variety that is used mainly in education, literature, law and mass media in the Arab World, the authors of the study who are PhD holders of linguistics and native speakers of SA were the informants of the data analyzed in the study. The findings of the study showed that SA involves six types of syllables which are CV, CVV, CVC, CVVC, CVCC, and CVVGG. The foot type of SA is trochaic; hence it is parsed from the left to right. The study also showed that SA involves a default-to-stress system since stress is commonly assigned to the rightmost heaviest syllable, or if a heavy syllable does not exist it will be assigned to the light leftmost one. Stress is, therefore, highly affected by syllable type and location. The study revealed that stress assignment system of SA is predictable and could be accounted for by utilizing a limited number of universal constraints. The following constraint hierarchy was developed to explain stress assignment in SA; Culminativity; *[delta]>>WSP>> EDGEMOST (?H; R; Word)>> Nonfinality>> EDGEMOST (?L; L; Word). Finally, further studies are recommended to investigate the interaction between stress assignment and other syllable-based phonological processes to provide a full account of the phonological system of SA from an OT perspective.