This study presents a comprehensive comparative analysis of verbal affixes in two Austronesian languages, Riau-Malay and Sundanese, with a focus on their morphological, syntactic, and semantic properties. Both languages are spoken in the Indonesian archipelago, and while they share certain linguistic characteristics, they exhibit intriguing differences in their verbal affixation systems. This study aims to contribute to the understanding of linguistic diversity within Austronesian languages and to reveal on the mechanisms underlying verb formation in these two distinct linguistic systems. By comparing and contrasting the verbal affixation systems in these languages, this study aims to reveal striking differences in terms of affix types, attachment patterns, and grammatical functions. The analysis explored the morphology of verbal affixes used in Riau-Malay and its comparison in Sundanese. It identifies clear distinctions in the ways affixes are employed to mark tense, aspect, mood, and other grammatical categories. Furthermore, the study also investigated the syntactic roles of verbal affixes, exploring how they affect word order and argument structure in sentences. This analysis exposes intriguing patterns of valency-changing operations in Riau-Malay and Sundanese. The findings of this study are expected to enhance people’s understanding of Riau-Malay and Sundanese and to contribute to the broader typological and theoretical discussions in linguistics. The comparative analysis of these two languages provides valuable insights into the ways in which languages within the Austronesian family can diverge and adapt to their unique cultural and historical contexts. Ultimately, this study may be valuable to advance our knowledge of linguistic diversity and variation, offering a deeper appreciation of the intricate web of languages that shape human communication in the Indonesian archipelago and beyond.