This study investigates phonetic and phonological factors which influence the degree of vowel-to-vowel coarticulation in Korean and English, especially around palatalization rules. Two phonetic factors and two phonological factors were examined in investigating the degree of anticipatory or carryover coarticulation in VCV sequences. The phonetic factors were the intervening consonants (alveolar stop vs. (alveo)palatals), and the second vowels (/i/ vs. /a/); the phonological factors were the effect of palatalization, and the lexical status of palatalization (lexical vs. postlexical palatalization). Ultrasound imaging techniques and F2 measurements are employed to see how much further front the articulation of V1 in V1CV2 sequences is due to influence of V2 across the consonants. Ultrasound images of vowels and their F2 values were quantified and statistically analyzed with ANOVA.First, it was found that V1 in V1CV2 sequences in Korean was articulated further front when intervening consonants were palatals than when they were alveolars, while there was no difference in frontness of V1 between two consonantal conditions in English. This indicates that Korean palatals are a stronger barrier to vowel-to-vowel coarticulation, while English alveopalatals are not. Next, V1 in both languages was articulated further front when V2 was /i/ than when V2 was /a/. Third, we had striking findings that palatalization rules caused stronger vowel-to-vowel coarticulation than in nonpalatalized words. Results showed that V1s were articulated further front across derived palatals than across underlying palatals in V1Ci sequences. Last, it was determined that V2 was articulated further front in words which underwent postlexical palatalization than in words which underwent lexical palatalization. Such findings indicate that postlexical palatalization causes greater gestural overlap than lexical palatalization, showing stronger degree of coarticulation.Based on the experimental results that phonetic details such as the degree of vowel-to-vowel coarticulation are highly conditioned by the lexical status of palatalization as well as the application of palatalization, I suggest a unified model of phonology and phonetics, using feature-and-gesture based OT frameworks. Second, I follow the proposal that abstract intergestural timing relations should be incorporated into phonological representations either in the input or output (Cho 1998, Gafos 2002, Yun 2005b).