This paper investigates the effects of syllable structures on v-to-v coarticulation. It was hypothesized that open syllables (V#CV) would allow less v-to-v coarticulation than closed syllables (VC#V). Languages with simple syllable structure (Thai) would allow less v-to-v coarticulation than languages with complex syllable structure (English). /C1V1#C2V2/ and /C1V1C2#V2t/ sequences were recorded from six native speakers in Thai and English. F1 and F2 frequencies were measured. Results show that English consistently allows more v-to-v coarticulation than Thai, but open and closed syllables do not affect v-to-v coarticulation differently. The results on open and closed syllables are compatible with Öhmans model of coarticulation.