The Human–Computer Interaction era contrived the researchers to work on speech and languages to develop interactive interfaces. A speech synthesizer is one such interface facilitating people to amalgamate with the digital era. The present work is focused on developing a Letter-To-Sound mapping for a Tamil speech synthesizer, which is an intriguing task due to the script to sound mapping irregularities in Tamil. Tamil is a syllable-timed language, hence a new syllable centric rule-based approach is formulated in the present work with a more extended set of rules than the existing rule-bases in the literature. This proposed rule-based system outperforms the existing rule-based systems with a low Character Error Rate and High Mean Similarity Score. © 2018, © 2018 IETE.