Utterance-final lengthening is a well-documented cross-linguistic phenomenon. While previous studies have noted its presence in Thai, systematic and empirical investigations remain limited. This study addresses this gap by conducting an acoustic analysis of utterance-final lengthening in Thai, using data produced by native speakers. Four frequently occurring polysemous Thai words—‘dai’ /dâːj/, ‘hai’ /hâj/, ‘pen’ /pen/, and ‘laeo’ /lɛ́ːw/—were selected and embedded in sentences designed to place them either medially or finally. These sentences were produced and recorded by twenty-one speakers of central Thai. Acoustic measurements and statistical analysis of the relevant speech tokens revealed that word rime durations in utterance-final positions were, on average, 3.5 times longer than in medial positions. The lengthening effect in final positions was so substantial that it considerably masked the temporal difference between function and content words. Interactions with other factors, such as vowel length, lexical tone and word type were also examined. These findings are expected to provide preliminary information on Thai utterance-final lengthening, contributing to the prosodic analysis of Thai and offer insights for cross-linguistic typological research.