Thai has its own distinctive alphabetic script with syllabic characteristics as it has implicit vowels for some consonants. Consonants are written in a linear order, but vowels can be written non-linearly above, below or to either side of the consonant. Of particular interest to the current study are that vowels can precede the consonant in writing but follow it in speech, hence a mismatch between the spoken and written sequence occurs. In order to investigate if there is a processing cost associated with this discrepancy between spoken and written sequence for vowels and the implications this has in relation to the grain size used when reading Thai, eye movements of adults reading words with and without misaligned vowels in sentences using the EyeLink II tracking system was conducted. Twenty-four university students read 50 pairs of words with misaligned and aligned vowel words matched for length and frequency embedded in same sentence frames. In addition, rapid naming data from forty adults was collected. Data from forty children 6;6-8;6 years old reading and spelling comparable words was also collected and analysed for errors. Results revealed a processing cost due to the more severely misaligned words where the vowel operates across the syllable, and gives support for a syllabic level of segmentation rather than phonemic for reading and spelling in Thai adults and children.