This study investigates the effect of prefixation on the syllable and syllabification in Najdi Arabic. It mainly addresses the role of prefixation on the syllable in this variety of Arabic, providing a prosodic representation of it within the context of rule-based phonology. The paper provides a review of the phonological processes that deal with prefixation phenomena in Najdi Arabic, whose domains of application are somewhat subject to syllabification processes and the syllable structure. To achieve this, the paper discusses the three types of prefixation in Najdi Arabic: (a) nominal prefixes, i.e., the definite article /ʔal/ and prepositional prefixes (predominantly fi- ‘in’, and bi- ‘in/at’), (b) the agreement-related prefixes, i.e., verbal prefixes and (c) the adverbial prefix /ʔib-/ ‘with’, which is prefixed to the host noun and changes its grammatical category to an adverb. The results show that each type of prefixation has its own functions, which are essentially related to the type of the host it attaches to. For instance, the prefix /ʔib-/, which is the Najdi Arabic adverbial marker, is a stress-bearing morpheme, given that it is a heavy syllable on its own, which attaches to the initial position at the very beginning of its nominal host.