Several characteristics of the Thai writing system make Thai graphemeto- phoneme (G2P) conversion very challenging. In this paper, we propose an Example-Based Grapheme-to-Phoneme conversion approach. It generates the pronunciation of a word by selecting, modifying and combining pronunciations from syllables from training corpus. The best system achieves 80.99% word accuracy and 94.19% phone accuracy which significantly outperform previous approaches for Thai.